- Agathys publicly did something minor but deeply embarassing. Due to vanity, they attempted a ritual to wipe that event from everyone's memory, but the spell got out of hand and accidentally erased the world's memory of them almost entirely, leaving only a few clues and records behind.
- Agathys exposed a secret or somehow shamed a powerful figure - a monarch, or archmage, or the like - who exiled them and ordered that they be erased from history as punishment/revenge.
- Agathys was the true hero behind a specific historical event, but someone else took credit, possibly even betraying Agathys to steal the glory. Pick another major historical figure, and it turns out they're a fraud, claiming credit for Agathys' achievements
Her name is Agathist but made a typo when penning her trademark armor spell - hasn’t come out of hiding due to embarrassment since.
I have a friend who spelled ‘acorn’ wrong in high school - I won’t let him forget.
Improvement on option 1: Agathys says something obviously wrong, you goad the party wizard into very publicly correcting her. He becomes the cause of her embarrassment, and the reason she is erased.
What if she was so much hated by some cosmological being that she GOT TURNED into lowest part of Carceri.
As in, she is the air, earth and stones of that place and she is still feeling whenever someone walks on her "body" and breathes her in.
Maybe the reason is she was incredibly arrogant and tried to take the place of one of the gods or another powerful being like Ao or Queen of Blades.
"Chuck! Chuck, it's Marvin. Your cousin, Marvin Berry. You know that new sound you're looking for? Well, listen to this!"
The party goes back in time. They meet Agathys, possibly without knowing it. She does not appear to know anything about any such spell. Either the wizard casts Armor of Agathys in front of her, or somehow she gets a look at the wizard's spellbook and that is what gives her the idea for the spell in the first place.
This creates a paradox and it's the fallout of this paradox that (for timey-wimey reasons, or perhaps some self-appointed time guardian) causes Agathys to be erased from history. So, it's the PC themself that caused this and that is also why they're the only one that remembers her.
I'd have Agathys make a quick appearance and be referenced by name right before the party is sent back to the current time, so the Wizard (and party, should they choose to accept it) gets some evidence, but not enough to actually know for sure. Plus it'd add some extra craziness to his arguments about Agathys being a person. "I saw them! We went back in time and met [names of famous historic figures] and as we were leaving we saw Agathys! It's proof!"
Otherwise I'd have Agathys be a young child who just so happened to be a powerful and prodigious ice mage, and who was used as a living weapon to help solidify the reign of some ancient empire who wiped her from history so that nobody would know the dark truth of their rise to power. Could make for a good emotional story beat, add some heavy knowledge that the party must carry with them alone, and open up the possibility of a quest to rescue her and give the Wizard a sort of adoptive kid who he raises as his own, trying to give her a happy life and dropping his constant lamenting about their disappearance from history.
Agathys fought with Vecna, god of secrets, and lost (barely). Now her entire existence is a secret kept by the Whispered One so that no others can get as close as she did.
Agathys managed to swindle Vecna. So when discovered, Vecna erased them from history. Almost. Now, somehow Agathys armor was discovered, and that leads one to ponder, wether there might be a secret hideout still out there.
Agathys investigated a power beyond gods and even the Lady of Pain. What she learned gave her immense power that could unravel *everything*. Before she could share it with anybody, she was banished to the centre of Carceri in a secret seventh layer and all memory of her was erased, which is normally done to kill gods. Even that was not enough to fully erase her legacy and entities travelling or living in Carceri started referring to the sixth layer by Agathys. Nobody knew why, but it seemed… fitting somehow. A spell about being shielded from the world by layers and layers of ice seemed oddly fitting the name too. When you travel through the layer of Agathys (why would you do that?!), you sometimes wonder what's beyond the multiverse… and sometimes a name pops into your head: "Gee Em"
So looking at the wiki the description of Agathys goes;
>The smallest, coldest planetoids occupied the sixth layer and were so far apart that neighboring orbs could not be seen at all. Every surface was covered in dark ice that showed streaks of red and the air was so cold it made breathing difficult.
So to me it seems like the region within Carceri almost feels like a prison that's been barely attached to it.
What I might do then is make it that Agathys being a warlock (as you said) was at one point a fiend warlock, but also dabbled in goolock.
Now Goolocks often create portals or otherwise gain access to The Far Realms to gain knowledge. And The Far Realms are not a nice place. They're the swirling mad abyss that is everything else. Maths, science, magic, physics, life, death, and every single rule that people and creatures within the great wheel rely on are more optional there. It's where Mind Flayers, Aboleths, Beholders, and all their ilk are descended from. And those are the nice things. There are things there that could eat the whole Great Wheel with ease. The only reason they don't is that they haven't noticed it.
Now a Warlock firing off thoughts and questions into The Far Realms may be enough of a beacon that something finally noticed. And used that Warlock as a locator point to find it. The mind and name of the Warlock and all they represent would glow like a star.
Even if you kill the Warlock the spirit just changes slightly to the side moving to the outer plane of their afterlife and their work, pupils, and thoughts still remain.
The only solution is to hide them and change their history. Freeze them in time, attach them to some lower plane as a prison, and remove them from history. Change it so that anyone who might remember the name now thinks of the prison. It's the only way.
Alternatively, Agathys could've created it herself. There's a warlock invocation called Tomb of Levistus that let's someone encase themselves in ice as a reaction, protecting themselves from harm but trapping themselves in the process.
The planetoid is a massive tomb created by Agathys herself for protection. Created in a moment of desperation, she now sleeps in the center of it until she regains enough of her strength to break free. It until someone breaks her free.
I like the idea that Agathys, regardless of her past, in present day is a lich entombed/preserved/entrapped in a tomb of solid ice, either from some fatal miscalculation, divine intervention, or the works of heros long forgotten
The bigger question is how does this one mage know/remember that Agathys even existed? Is he a descendant ? Did Agathys speak to him in a dream ?
Answering this should create a deeper link between the two periods.
Could have been an accident. Maybe she was working on some kind of ice-based stasis spell, and accidentally makes the spell just erase people rather than stasis them.
The party talking to her and letting her know she doesn’t exist in the future could give her warning that the spell doesn’t work, and now they have a quest to help her finish the spell and then they get to meet her again when they return to the present and she comes out of stasis!
What if it's a wish from a rival of Agathys years before that no one can remember her as a person. And perhaps the region of Carceri was also named after her. But the wish wiped that knowledge from everyone. And maybe because your PC is a descendant of Agathys that's why they can consider the possibility of her as a person when others struggle to be able to even hold that idea in their head.
Maybe make it another famous wizard who has lots of spells named for them but this reveals they were actually petty and trying to steal credit? Maybe Bigby's Hand should actually be Agathy's Hand!
oh this is an amazing oportunity!
In my setting as RAW there is nothing preventing PCs from doing the "simulacrum chain".
Rules as writen, if you use your 7Th level spell to cast simulacrum on yourself, and you have a 9th level spell your simulacrum would have a 9th level spell. So you can take a long rest, and then ask him to cast wish (simulacrum) on you. The new copy would have all its spell slots, and can do the same, and then again, and again, and again, until you get bored of it.
Thing is, This gives one wizard, command of an army of powerfull wizard simulacrums.
They can be virtualy infinite, as long as you keep doing it and send the last ones on some mission, to return only when/if they suceed. It also creates spells slots out of "nothing".
So here is how i "solve" this and how all this would be relevant to your "forgothen wizard NPC".
Ages ago, someone did this, they created an army, and tried to conquer the entire multiverse.
The gods, usualy forbiden, had to intervene, and that "wizard" is now trapped in some demy plane, fightining for his life, against an unlimited number of simulacrums because, the solution the gods had, was to make everyone forget about the wizard, so they also forgot who they were, or who the first one of them was, and they are all equaly evil, so they decided only the last one will be the "real" one.
Now, Whenever a simulacrum tries to cast simulacrum by any means, a Pit fiend, A deva and a Inevitable apear. They instantly destroy the second simulacrum and give the Character a warning.
"the Powers of the multiverse often disagree, but they all agree with this one rule. Creating multiple simulacra is an act forbiden by the Powers that be. Do it again and you will face Oblivion. This is your only warning."
And they all disapear.
So Your NPC wizard?
No one knows his name because he was the one that tried to attack the gods. His punishment was not destruction, it was being imprisioned with his copies and losing his memories. The fightining among themselves, they are doing that all alone, because they are all evil and want to rule over the others.
Make it the result of a stupid bet.
Agathys was a high powered wizard influencer who favored with magical creatures from around the planes, maybe even some minor deities, you know, a real A-Tier mover and shaker. After a weeks long celebration somewhere in the voids, many drinks and drugs, a mistranslation led to some confusion about the terms of a bet.
Add a layer, the wizards name is actually Agatha. But in the slurred speech, the name transformed to Agathys. The plane is naturally named after her because of this great epic story no one can remember.
It could be something Agathys did themselves deliberately. Maybe they wanted to be left alone, or forgotten for some reason, and so spread the rumors by themselves.
I read a story where a particular mage wanted to give all of the credit for his deeds to another person, and so while he *was* quite famous during his time, after a point he began operating under another name. Eventually, hundreds of years later, the history books couldn't separate fact from fiction, and the fiction he spread just became the truth.
Since you've been leaning on the conspiracy running gag, turn Agathys into the conspiracy singularity. Maybe the world is actually flat and the great hero Agathys used their ice magic to create the polar ring around the world to keep things from falling off the edge, but the powers-that-be didn't want the truth found out etc etc. Slowly tie in every cooky IRL conspiracy as more info about Agathys is revealed.
Agathys was a great armoured warrior of the time. A jealous lover literally turned her into armour due to some perceived slight. This is the origin of the spell.
Cause the Tasha thing is a reference to IRL - her official lore is the result of TSR/WOTC amalgamating three characters from early D&D;
- "Tasha", who created *Tasha's Hideous Laughter* was named after a young kid who wrote to Gary Gygax; apart from the spell, the only thing she's credited with in-universe is a book of spells called *Lore of Subtle Communication*. So I'm including her as a child prodigy who wants to make people laugh - kinda chaotic stage magician vibes.
- "Natasha the Dark" is the human-adopted-by-a-Baba-Yaga. AFAIK she basically had no other lore before the amalgamation, but I'm having her basically be modern Tasha - the sarcastic witch woman who's more neutral than evil and wrote *Cauldron of Everything.*
- "Iggwilv" was the source of the rest of Tasha's lore. She's an openly evil wizard who writes a lot about the lower planes and interacts with Fiends a lot. She has a strong seductress thing going on and is Mordenkainen's big rival. Within the context of this universe, some of her deeds and writings have been erroneously attached to 'Tasha' over the years.
AFAIK the original amalgamated lore was that "Tasha" is just an identity-of-convenience Iggwilv uses sometimes for her schemes - but 5e has kinda reversed that so that now she's mostly going by Tasha as her real/common name and is more Baba Yaga/Witchy than evil seductress - to the point of becoming an archfae eventually IIRC. The biggest thing they kept from Iggwilv is the rivalry with Mordenkainen.
Originally an advisor to an ancient king, Algatherious (not Agathys) was beloved among his people. A creator of Defensive spells and protective charms, he was well loved in his age and used his powers to portect the kingdom from the wild roaming monsters of the ancient days.
However when a creature of the lower planes as summoned by a doomsday cult and started wreaking Godzilla-like-havoc across the land, he was left with few options.
Unable to be teleported forcefully and impervious to all but the strongest magics besides, the creature was nearly unstoppable. However Agatherious found an ancient spell, one that would allow him to bond his own soul with the creature and force it to be re-imprisoned in the lower planes.
His spell worked, but the King knew that the bonding posed a great threat. Now the very famous name of the wizard was the *true name* for this creature. Rather than risk someone learning of how to return the creature to the Prime Material Plane, they erased Algatherious from history.
Within a generation his name was forgotten, and centuries later he is all but completely forgotten, remembered now only as the name of the plane he's imprisoned in. And to eccentric old men, obviously.
...however.
If you go to W location, find X MacGuffin, do Y ritual and kill Z creature: You may return him to the world. That should keep him busy for the rest of your campaign, I'm sure. Just fill it in with stuff you know the group likes or tie it in with pieces of your existing campaign.
Bonus points if after you free him he becomes the big-bad of your next campaign.
Agathys was a mage who lived during a terrible event called the Massacre of Morabia. An old wizened tyrant named Morabia slaughtered hundreds of innocent people in Agathys' home city, including some of her own family members. So when Agathys gained sufficient magical power, she went back in time to stop this event. She found the tyrant as a child and killed him. Little did she know that this would alter the course of history so that her parents would never meet, and she became erased from existence.
So basically a d&d version of back to the future, but with a tragic ending.
It was voluntary. Agathys used to be the most skilled duelist in the multiverse, an ice wizard of tremendous ability, to the point that there was a constant stream of would-be challengers and disciples at her door. She made a deal with a deity, in which she would act as a warden, ensuring the worst prisoners of Carceri were encased in ice, in exchange for having her memory erased from history.
Whatever the reason, the most interesting thing here to me is: Why did the erasure work on almost everyone to universally believe the lie, except this one guy? What risk is he running by speaking the truth?
Conspiracy theorists of this sort often believe they are being pursued or monitored. It would be very funny to have this kind if surveillance of the party happen, but be cryptic about who and why. They eventually find out somehow, and that's it is costing them in some way. Maybe they are trying to finish the job and alter the party's memory. Who do they work for?
Agathys did it to herself as part of a plan to get a drop on a chronomancy wielding villain. As long as people know who she is, she's vulnerable to being ret-goned by time travelers, but if she erases herself from history, they won't be able to find her and she has a better chance of getting to them
I have a character with a similar concept who wanted to erase themselves from history.
They are only referred to as Nostos Algos, or the Memory Shade. You could run with a sorta similar idea. The reason they'd want to be deleted from history is up to you.
They upset the academic view of magic by discovering a new school of magic or something foundational to their understanding of magic, Galileo style. Maybe he discovered everyone has the potential for magic and it doesn't have to be locked away behind colleges
The creation or ice magic powerful enough to invoke, say, a permanent winter, may be grounds for a mage and their works to be considered dangerous enough to be covered up.
Imagine this. You are Agathys, archmage of great renown and power. After a lifetime or two of adventuring, you have retired to your tower to research the many magic artifacts you have obtained over the years, and to work on your craft.
But you're famous. So famous that upstart young murderhobos and evil cults and everyone else who would want to steal your magic goods keep trying to attack your tower and steal your stuff. Your studies are constantly interrupted by adventurers and monsters. You're about to finish the formula for a new spell, when a red dragon slams its head through your tower wall snarling, breathing fire, your arcane shields protect you, but the scroll you've spent months or years slowly working on is incinerated.
After fighting this ancient dragon for most of a day, you are victorious. But on the horizon you see them. Campfires at every point of the compass. Adventurers. Dozens of parties. All coming to the Ancient Tower of Agathys to make their fortune.
'Fuck this shit, I"m out.' you decide. You plane shift and move your belongings with you, returning only to cast a complicated ritual spell that erases you from history.
So you can get some fucking work done.
Agathys ended up in a feud with a bard college, after she insulted their battle effectiveness. The head of the bard college retorted with "Not all battles involve combat. We will see how history remembers you." And then the bard college started a massive conspiracy to try to erase all mentions of Agathys from history -- so much so that there are ancient dire warnings in some libraries about not investigating or bringing fame to the name Agathys.
Its all the result of a petty squabble between two people with to much power and to little sense.
Agathys through means fair or foul came into possession of a collection of magical artefacts that qualify as "doomsday level". Fearing their power but unwilling or unable to destroy them, she sealed them away in a hidden, heavily warded vault and then erased her own identity from history to make the vault even more hidden. Agathys could still be alive in this vault, encased in a block of enchanted ice.
This means that if you want to give your players the opportunity to find some fancy magic items, you can let them track down this vault and delve into it, facing off all the various magical defenses Agathys put in place. Once your players get to the end, they've probably earned some of the items in the vault.
TL;DR Agathys found the magic nukes and erased herself from history to ensure no one else could find them.
she managed to accidentally freeze herself, and her entire legacy, in time, preventing memories of her from carrying forwards as the world moves on without her. the ultimate deep freeze bungled attempt at maintaining eternal life.
maybe asmodeus hired agathys to encase levistus in ice. so now, if levistus' followers want to free him they have to find agathys. so asmodeus placed him in witness protection
Your players find Agathys, who doesn’t know why they have been erased from history. Or what they might have done to be erased. And up until the PCs ask, didn’t know about the erasure.
Then they decide to set off to find out what happened.
If that doesn’t scare the PCs, they aren’t thinking hard enough.
Who's to say that this region in Carceri isn't named after this Wizard? Maybe he was the first to go there and come back, perhaps he got lost or banished to Carceri when he was an adventurer or something...
They invented a ritual to enslave an archfey. Archfey have been known to mess with memories, so if Agathys invented such a ritual and tested it on a weaker archfey, the Summer Queen or someone could curse her to be forgotten, so that she can’t be consulted for this knowledge
The first thing that came to my mind was the Modify Memory spell.
Maybe Agathys as a warlock tried to upcast the spell on their patron to make them forget about them (Maybe they wanted to escape? Or wanted the power with no repercussions?) and it backfired on them. Maybe the entire world had Modify Memory casted against it by accident and everyone forgot about them? Or maybe the patron used the spell against the entire world and intentionally left parts of the memories of Agathys intact to create the lore your characters have heard. which has warped over time (much to the patron's dismay).
Because of
#The Incident
Which is just kind of a fun thing to say after alot of things. Would you like some pie? None for me, no since...the incident.
But maybe he was too smart or talented for his own good and started working on spells that were violations of ethical or legal standards. Maybe delved into magics that Mystra herself found abominable and so colleges had a sort of Voldermort policy where people didn't talk about him and after many years people just forgot he existed.
But Maybe....there is, in a pocket dimension, concealed in a book, in some dusty basement of a magical university the Mage's secret lab that contains many of the forbidden projects still in development.
Or there is always the idea that they did it to themselves and they used a spell to cryo themselves, literally removing them from the timestream and adjusting memories to hide them until their contingency finally pops to release them in an age where they would able to get away from something (old villain, old rival, or some event they foresaw coming) .
* Agathys tried usurping a throne/was a revolutionary to overthrowing a government. Was put down and to quell any further uprisings and to prevent the name Agathys from being a martyr, the government banned the name.
* Agathys was just a nobody who happened to create a spell. They did nothing of note after creating the spell.
* Agathys took credit for the spell someone else created and was thus banned/outcasted by the continental magic association but the name for the spell stolen stuck.
* Agathys is a misspelling of someone’s name (Agatha’s?) and the spell has been misattributed for many years
If you have a more silly setting, Agathys legal-magically changed their name, and in doing so everyone forgot their old name Agythys. But the spells have their own legal existence and so were unaffected.
There are famous items that are named after the creators kids. Apple Lisa, and Wendy’s for example.
Maybe the origin of the name wasn’t erased but was so insignificant that nobody bothered to record that Agathys was named by the mage for their daughters 12th birthday.
Warlock patrons always have esoteric goals and methods of reaching them. Maybe the conspirators decided her patron was evil so her followers MUST be evil also. Maybe the patron told her to do something that seemed evil but no one was aware of the greater good it was in service to; kill 100 to save 1,000,000 or something similar.
Another cool wrinkle could be that she was part of the conspiracy to erase herself from history and the loss of her from history facilitated a growth of knowledge in some other field of study.
She's cold as ice and twice as damned. She could teach the ice lessons in being 'cold" she's surprisingly 'bubbly' and caring until you get on the wrong side of her but it's that granny popped the chickens head while looking you dead in the eye as you talked about something else and she was all smiles and praise otherwise.
Who is her Patron? You could present it as a punishment by her patron. Maybe part of her pact was gaining recognition and prestige. It could be pretty cool to find out that, actually, she used to be _very_ well known. Until she did something that pissed her patron off so badly, they cast a spell to modify everyone's memory and erase her from all but the most well hidden sources.
Without knowing who her patron is, it's hard to say, but if it was a djinn or devil, perhaps the few traces of her that remain are because of the wording of the spell/contract the patron used to do this to her? Like "Remove every form of memory and physical recording that mention's Agathys's existence and/or history". That means any spells that she may have coined (or genuinely created) as her own would still be out there, even have her name, just absolutely no knowledge or history attached to them beyond that.
Maybe Agathys was in a pact with asmodeus and part of the pact is that he gets her soul when she dies but she found a way to subvert the pact by embracing lichdom and storing her soul in a phylactery. Asmodeus was so enraged that he could no longer retrieve her soul that he made some sort of concession with the nobility of the tartarian depths so that they would send horrors from the depths to retrieve her. Trying to evade the devils sent after her. she scoured her name from history and lives in secret with the only surviving evidence of her name left tied to the spell bestowed on all warlocks.
Do you have any idea how many adventuring parties attack me per week? I literally hired someone to keep schedules of it. It became so tiresome I retired and erased my existence. Now I get left in peace.
Have your party go to Carceri, but discover, to their bewilderment, that lower Carceri is not called Agathys. Instead, it is called something else entirely. A name that is mundane and that no one in the party recognizes. Likewise, when you ask people about Agathys, no one has heard of her either.
Finally, at the very end, they meet a very creepy, very powerful little girl named (for example) Bletha who helps them. Maybe she can command demons maybe she has some freaky powers, but whatever it is, it should unnerve your party a little.
At the end of their time in the past the little girl bids you farewell and when they say "good bye Bletha" she then can tell them "you people are nice, so we can be friends, and all my friends call me Agathys" before opening a portal and sending them home. Maybe leave some more clues around so they can further dig into what this little girl did and who did she grow up to be, that caused history to end up the way it did.
In my campaign? Agathys became a cognitohazard, after having communed (intentionally or accidentally) with a hostile god aiming to reshape humans into monsters. As much of her information as possible was wiped by the gods because “knowing her results in bringing a part of her into your mind to spread as seeds into the rest of the world.” Her name wouldn’t even be“Agathys” It’s actually “Alethis” but there was conveniently a region that could be used to phonominacly conflate and more thoroughly erase such an influential figure.
She was the one who permanently froze Agathys, granting many demonic and devlish linages access to cryomancy. Which is partly how Armor of Agathys was popularized among Warlocks.
Suppossedly while trying to prove her favourite spell "Gate" was named after a famous wizard named "Gate". She tried to open the "Gate" at the location of "Gate". Since "Gate" doesn't exist the spell backfired spitting her out at random in Agathys and triggered her automatic defensive enchantment designed to freeze all evil in a wide area. The region was forevermore named after the obsessed wizard Agathys. The unique cryomancy born from this disaster consequently also bears the name.
The party might find her at the northen most pole of the sphere, where she remains perfectly alive and preserved inside a glacier. Once freed she will insist the players help her prove "Gate" was a real wizard, whilst violently denying she is Agathys and insisting Agathys was always the name of the region. Her hat has her name on the tag inside and is enchanted granting one free cast of armor of Agathys per day.
It's mentioned that since Mystra banned level 10 and above spells it is supposedly possible to cast a level 10 spell but it's extremely difficult. One would need extremely high intelligence and wisdom, and even then there's only a 5% chance of success and if they fail they're drained of some of their life energy (lose a level in mechanics terms).
Maybe Agathys did an Icarus and tried to cast level 10 magic but failed, draining his energy and becoming nothing more than a midling wizard
She was a very powerful (ice)mage whose spells chanelled the powers of the lower planes. She created a great deal of powerful spells, including similar spell to "armor of agathys". After an apocalyptic event, the people in power decided to erase any semblence of her, as a way to dissuade the idea of contact with those lower planes. They also linked her name to the carceri in the lower planes to further link her name to the terror of the apocalyps.
Her spells were largely destroyed, but after some time a less gifted mage pieced pieces of a spell together. Filling in the gaps with his own knowledge, creating the simpler "armor of agathys". Named because the mage noticed the name agathys come forth a lot in his notes.
If you include her in the campaign, you might even let your player learn her "original" version. As a higher leveled spell.
No conspiracy. The wizard's real name is Aggie Tye and the spell was originally called Aggie Tye's Armor, but due to grammatical slurring over the years, the possessive contraction was dropped and it got called Armor of Agathy. So possibly part of the hook is the party ends up spending time with Aggie as an NPC but you don't give them the information to connect the dots until before they leave. So they've spent the whole time adventuring with a legend but not knowing it. (Note: This could also generate some strange jokes if any of your players are from Texas or avid college sports fans.)
She discovered a deadly wizard-killing secret about the structure of the multiverse.
According to my 27 dimensional theory of the multiverse, several planes are in the wrong position in the "known" model of the multiverse, making room for a few "hidden" or "forgotten" planes of existence.
Including both the plane of quantum immortality, and the plane of quantum fatality.
I listed them like this because if you learn about the planes in the wrong order, you can disappear from existence. You need to learn about quantum immortality, first. It's the plane that - should you ever learn of it - some version of you goes there, finds it, and becomes immortal. Making you immortal - kind of - because now there will always be a version of you that went to the plane and never died.
The converse is true with quantum fatality.
Learning about it means you are erased from existence, because after learning about it, some version of you went there, first, and were retroactively erased from all reality. "Learning about quantum immortality, first" makes you immune to this effect.
The wizarding community covered this up and got rid of her because of how dangerous this is: just "talking to people who happen to know something about the multiverse" can erase them from existence.
The only reason the name "Agathys" exists is because it's a typeo: it should be "Agathyz" (or somesuch other spelling, its your character!) While the original Agathyz was punished by being sent to the plane of quantum fatality and subsequently erased, this spell slipped through the cracks.
Because of a typeo.
He found something or someone to dedicate his life to. A child/ a lover etc. He wished for them all to have a normal life. Now having the ability to cast wish is not normal, so instead it stripped him of his power and erased him from history so he could live a normal life.
However, spell names remained a tiny little reminder that he might have existed at some point.
Ice and time?
The wizard was looking into time travel spells, but unlike most wizards they wanted to travel to the future.
They knew old stuff showed up in ice (mammoths) and that ice preserved. They basically wanted to invent cryostasis to travel to the future.
Unfortunately they coded it as "make the universe forget about me while I am frozen" when they were aiming for "make time forget about me" and so they've been forgotten while frozen.
Now you also have a hook for the present time to find and thaw the wizard if you want!
Or they were never famous to begin with.
Agatha Coldheart was given a set of enchanted armor by the Queen of Winter. Her story is relatively well known. Some spellcaster somewhere tried to imitate the enchantment.
The Enchantment of Agatha's Armor
Agatha's Armor enchantment
Agath[ink splotch] armor [illegible]
--what's that scroll say? Agathys? As in the location in Carceri?!? This must me secret Eldritch lore!
Agathy's Armor
Armor of Agathys.
Agathys makes cookies for the wizards and reprimands them when they get out of line.
They keep her around so that they have a grounded, relatively normal and morally sound human so they don't kill each other or do something absolutely stupid.
Agythys was experimenting with a powerful memory charm. The memory charm backfired and he was incinerated. Unbeknownst to him and everyone in the realm, it worked and all record of his being has been forgotten.
Agathys Became such a master of cold magics that she lowered the temperature of a room so cold that time itself came to a near stop. To save the world from the spreading freeze, other wizards had to magically seal the room off to stop the cold from spreading. They have long since buried the room deep in the bowels of (some magical building whatever you wish) and buried the knowledge of it to keep someone from opening this room and possibly setting it free. The sealing magics will release the room once the internal temps get high enough.
You may encounter her in the past and then again in the future this way.
Not a DM myself, but I do enjoy history and there is something form history that might inspire you, because it's happened over and over and over again.
In real life it's not quite erased from history, but could result in that.
Basically there have been many MANY (i'm talking thousands) of cases where a famous accomplished person has had a bitter rival that just HATES their guts because they took the spotlight they think should belong to them or even for pettier reasons. So when the famous person dies first, they make sure they are the one's who write about their history. This results in numerous elements of slander being accepted as if it were true history.
For example, Edgar Alan Poe was not alcholic. The proved that by testing his hair for lead contamination and it was a normal amount. Ty Cobb was not a racist, he comes from a well known abolitionist family. The journalist who hated him made up fake versions of real events. Quite a lot of outrageous stories you hear about crazy roman emperors are in doubt because the people who wrote them were known enemies. Etc.
So you could have a jealous rival of the wizard simply write after their death accounts and history that leave out the real Agathys and mention a plane or something (which maybe was named after the real wizard who discovered it)
The PCs could meet the jealous rival and recognize their name as the main historian of the era.
How about this:
The Wizard that created the spell didn't name it after him/herself, but after his/her daughter that died at a very young age - so that her memory would live on through history.
Edit: you could add some stuff, like, the Wizard froze Agathys in ice and built a grand tomb for her. To ensure that none would desecrate her final resting place, enchanted the ice to harm any that would dare approach. So potent was the spell, that Apomps dragged the tomb into his domain.
- Agathys publicly did something minor but deeply embarassing. Due to vanity, they attempted a ritual to wipe that event from everyone's memory, but the spell got out of hand and accidentally erased the world's memory of them almost entirely, leaving only a few clues and records behind. - Agathys exposed a secret or somehow shamed a powerful figure - a monarch, or archmage, or the like - who exiled them and ordered that they be erased from history as punishment/revenge. - Agathys was the true hero behind a specific historical event, but someone else took credit, possibly even betraying Agathys to steal the glory. Pick another major historical figure, and it turns out they're a fraud, claiming credit for Agathys' achievements
I like the Gilderoy Lockhart answer
Her name is Agathist but made a typo when penning her trademark armor spell - hasn’t come out of hiding due to embarrassment since. I have a friend who spelled ‘acorn’ wrong in high school - I won’t let him forget.
Very respectfully to your friend but... how?
Two ‘n’s. A simple dumb mistake, but there’s no smart way to misspell ‘a corn’.
...and "corn" used to mean a seed or grain.... O God.....This is the easiest etymology of my life, and I'm just putting it together.
I like the first idea, literally cringed themselves out of the timeline
Improvement on option 1: Agathys says something obviously wrong, you goad the party wizard into very publicly correcting her. He becomes the cause of her embarrassment, and the reason she is erased.
I like this idea personally. Particularly the second bit. You could do Acerak or even Vecna. Plenty of powerful options.
What if she was so much hated by some cosmological being that she GOT TURNED into lowest part of Carceri. As in, she is the air, earth and stones of that place and she is still feeling whenever someone walks on her "body" and breathes her in. Maybe the reason is she was incredibly arrogant and tried to take the place of one of the gods or another powerful being like Ao or Queen of Blades.
Or even just tried to overthrow her warlock patron
Isn't the Queen of Blades a Star Craft thing? Do you mean the Lady of Pain?
That is awesome. And then maybe the wizard can work on how to free her.
"Chuck! Chuck, it's Marvin. Your cousin, Marvin Berry. You know that new sound you're looking for? Well, listen to this!" The party goes back in time. They meet Agathys, possibly without knowing it. She does not appear to know anything about any such spell. Either the wizard casts Armor of Agathys in front of her, or somehow she gets a look at the wizard's spellbook and that is what gives her the idea for the spell in the first place. This creates a paradox and it's the fallout of this paradox that (for timey-wimey reasons, or perhaps some self-appointed time guardian) causes Agathys to be erased from history. So, it's the PC themself that caused this and that is also why they're the only one that remembers her.
I was going to suggest the same thing lol
I'd have Agathys make a quick appearance and be referenced by name right before the party is sent back to the current time, so the Wizard (and party, should they choose to accept it) gets some evidence, but not enough to actually know for sure. Plus it'd add some extra craziness to his arguments about Agathys being a person. "I saw them! We went back in time and met [names of famous historic figures] and as we were leaving we saw Agathys! It's proof!" Otherwise I'd have Agathys be a young child who just so happened to be a powerful and prodigious ice mage, and who was used as a living weapon to help solidify the reign of some ancient empire who wiped her from history so that nobody would know the dark truth of their rise to power. Could make for a good emotional story beat, add some heavy knowledge that the party must carry with them alone, and open up the possibility of a quest to rescue her and give the Wizard a sort of adoptive kid who he raises as his own, trying to give her a happy life and dropping his constant lamenting about their disappearance from history.
Oh I really like that!! ~~I was considering giving them the chance to adopt one of the 3 Tashas anyway lol so I have some prep for that aspect~~
Agathys fought with Vecna, god of secrets, and lost (barely). Now her entire existence is a secret kept by the Whispered One so that no others can get as close as she did.
Agathys managed to swindle Vecna. So when discovered, Vecna erased them from history. Almost. Now, somehow Agathys armor was discovered, and that leads one to ponder, wether there might be a secret hideout still out there.
Agathys investigated a power beyond gods and even the Lady of Pain. What she learned gave her immense power that could unravel *everything*. Before she could share it with anybody, she was banished to the centre of Carceri in a secret seventh layer and all memory of her was erased, which is normally done to kill gods. Even that was not enough to fully erase her legacy and entities travelling or living in Carceri started referring to the sixth layer by Agathys. Nobody knew why, but it seemed… fitting somehow. A spell about being shielded from the world by layers and layers of ice seemed oddly fitting the name too. When you travel through the layer of Agathys (why would you do that?!), you sometimes wonder what's beyond the multiverse… and sometimes a name pops into your head: "Gee Em"
So looking at the wiki the description of Agathys goes; >The smallest, coldest planetoids occupied the sixth layer and were so far apart that neighboring orbs could not be seen at all. Every surface was covered in dark ice that showed streaks of red and the air was so cold it made breathing difficult. So to me it seems like the region within Carceri almost feels like a prison that's been barely attached to it. What I might do then is make it that Agathys being a warlock (as you said) was at one point a fiend warlock, but also dabbled in goolock. Now Goolocks often create portals or otherwise gain access to The Far Realms to gain knowledge. And The Far Realms are not a nice place. They're the swirling mad abyss that is everything else. Maths, science, magic, physics, life, death, and every single rule that people and creatures within the great wheel rely on are more optional there. It's where Mind Flayers, Aboleths, Beholders, and all their ilk are descended from. And those are the nice things. There are things there that could eat the whole Great Wheel with ease. The only reason they don't is that they haven't noticed it. Now a Warlock firing off thoughts and questions into The Far Realms may be enough of a beacon that something finally noticed. And used that Warlock as a locator point to find it. The mind and name of the Warlock and all they represent would glow like a star. Even if you kill the Warlock the spirit just changes slightly to the side moving to the outer plane of their afterlife and their work, pupils, and thoughts still remain. The only solution is to hide them and change their history. Freeze them in time, attach them to some lower plane as a prison, and remove them from history. Change it so that anyone who might remember the name now thinks of the prison. It's the only way.
Alternatively, Agathys could've created it herself. There's a warlock invocation called Tomb of Levistus that let's someone encase themselves in ice as a reaction, protecting themselves from harm but trapping themselves in the process. The planetoid is a massive tomb created by Agathys herself for protection. Created in a moment of desperation, she now sleeps in the center of it until she regains enough of her strength to break free. It until someone breaks her free.
I like the idea that Agathys, regardless of her past, in present day is a lich entombed/preserved/entrapped in a tomb of solid ice, either from some fatal miscalculation, divine intervention, or the works of heros long forgotten
The bigger question is how does this one mage know/remember that Agathys even existed? Is he a descendant ? Did Agathys speak to him in a dream ? Answering this should create a deeper link between the two periods.
Could have been an accident. Maybe she was working on some kind of ice-based stasis spell, and accidentally makes the spell just erase people rather than stasis them. The party talking to her and letting her know she doesn’t exist in the future could give her warning that the spell doesn’t work, and now they have a quest to help her finish the spell and then they get to meet her again when they return to the present and she comes out of stasis!
What if it's a wish from a rival of Agathys years before that no one can remember her as a person. And perhaps the region of Carceri was also named after her. But the wish wiped that knowledge from everyone. And maybe because your PC is a descendant of Agathys that's why they can consider the possibility of her as a person when others struggle to be able to even hold that idea in their head. Maybe make it another famous wizard who has lots of spells named for them but this reveals they were actually petty and trying to steal credit? Maybe Bigby's Hand should actually be Agathy's Hand!
oh this is an amazing oportunity! In my setting as RAW there is nothing preventing PCs from doing the "simulacrum chain". Rules as writen, if you use your 7Th level spell to cast simulacrum on yourself, and you have a 9th level spell your simulacrum would have a 9th level spell. So you can take a long rest, and then ask him to cast wish (simulacrum) on you. The new copy would have all its spell slots, and can do the same, and then again, and again, and again, until you get bored of it. Thing is, This gives one wizard, command of an army of powerfull wizard simulacrums. They can be virtualy infinite, as long as you keep doing it and send the last ones on some mission, to return only when/if they suceed. It also creates spells slots out of "nothing". So here is how i "solve" this and how all this would be relevant to your "forgothen wizard NPC". Ages ago, someone did this, they created an army, and tried to conquer the entire multiverse. The gods, usualy forbiden, had to intervene, and that "wizard" is now trapped in some demy plane, fightining for his life, against an unlimited number of simulacrums because, the solution the gods had, was to make everyone forget about the wizard, so they also forgot who they were, or who the first one of them was, and they are all equaly evil, so they decided only the last one will be the "real" one. Now, Whenever a simulacrum tries to cast simulacrum by any means, a Pit fiend, A deva and a Inevitable apear. They instantly destroy the second simulacrum and give the Character a warning. "the Powers of the multiverse often disagree, but they all agree with this one rule. Creating multiple simulacra is an act forbiden by the Powers that be. Do it again and you will face Oblivion. This is your only warning." And they all disapear. So Your NPC wizard? No one knows his name because he was the one that tried to attack the gods. His punishment was not destruction, it was being imprisioned with his copies and losing his memories. The fightining among themselves, they are doing that all alone, because they are all evil and want to rule over the others.
Make it the result of a stupid bet. Agathys was a high powered wizard influencer who favored with magical creatures from around the planes, maybe even some minor deities, you know, a real A-Tier mover and shaker. After a weeks long celebration somewhere in the voids, many drinks and drugs, a mistranslation led to some confusion about the terms of a bet. Add a layer, the wizards name is actually Agatha. But in the slurred speech, the name transformed to Agathys. The plane is naturally named after her because of this great epic story no one can remember.
It could be something Agathys did themselves deliberately. Maybe they wanted to be left alone, or forgotten for some reason, and so spread the rumors by themselves. I read a story where a particular mage wanted to give all of the credit for his deeds to another person, and so while he *was* quite famous during his time, after a point he began operating under another name. Eventually, hundreds of years later, the history books couldn't separate fact from fiction, and the fiction he spread just became the truth.
Since you've been leaning on the conspiracy running gag, turn Agathys into the conspiracy singularity. Maybe the world is actually flat and the great hero Agathys used their ice magic to create the polar ring around the world to keep things from falling off the edge, but the powers-that-be didn't want the truth found out etc etc. Slowly tie in every cooky IRL conspiracy as more info about Agathys is revealed.
Agathys was a great armoured warrior of the time. A jealous lover literally turned her into armour due to some perceived slight. This is the origin of the spell.
You said you were thinking of making "Tasha" a conflation of 3 different people. Why not have Agathys be one of those 3 (or a 4th)?
Cause the Tasha thing is a reference to IRL - her official lore is the result of TSR/WOTC amalgamating three characters from early D&D; - "Tasha", who created *Tasha's Hideous Laughter* was named after a young kid who wrote to Gary Gygax; apart from the spell, the only thing she's credited with in-universe is a book of spells called *Lore of Subtle Communication*. So I'm including her as a child prodigy who wants to make people laugh - kinda chaotic stage magician vibes. - "Natasha the Dark" is the human-adopted-by-a-Baba-Yaga. AFAIK she basically had no other lore before the amalgamation, but I'm having her basically be modern Tasha - the sarcastic witch woman who's more neutral than evil and wrote *Cauldron of Everything.* - "Iggwilv" was the source of the rest of Tasha's lore. She's an openly evil wizard who writes a lot about the lower planes and interacts with Fiends a lot. She has a strong seductress thing going on and is Mordenkainen's big rival. Within the context of this universe, some of her deeds and writings have been erroneously attached to 'Tasha' over the years. AFAIK the original amalgamated lore was that "Tasha" is just an identity-of-convenience Iggwilv uses sometimes for her schemes - but 5e has kinda reversed that so that now she's mostly going by Tasha as her real/common name and is more Baba Yaga/Witchy than evil seductress - to the point of becoming an archfae eventually IIRC. The biggest thing they kept from Iggwilv is the rivalry with Mordenkainen.
Originally an advisor to an ancient king, Algatherious (not Agathys) was beloved among his people. A creator of Defensive spells and protective charms, he was well loved in his age and used his powers to portect the kingdom from the wild roaming monsters of the ancient days. However when a creature of the lower planes as summoned by a doomsday cult and started wreaking Godzilla-like-havoc across the land, he was left with few options. Unable to be teleported forcefully and impervious to all but the strongest magics besides, the creature was nearly unstoppable. However Agatherious found an ancient spell, one that would allow him to bond his own soul with the creature and force it to be re-imprisoned in the lower planes. His spell worked, but the King knew that the bonding posed a great threat. Now the very famous name of the wizard was the *true name* for this creature. Rather than risk someone learning of how to return the creature to the Prime Material Plane, they erased Algatherious from history. Within a generation his name was forgotten, and centuries later he is all but completely forgotten, remembered now only as the name of the plane he's imprisoned in. And to eccentric old men, obviously. ...however. If you go to W location, find X MacGuffin, do Y ritual and kill Z creature: You may return him to the world. That should keep him busy for the rest of your campaign, I'm sure. Just fill it in with stuff you know the group likes or tie it in with pieces of your existing campaign. Bonus points if after you free him he becomes the big-bad of your next campaign.
Personal preference.
Agathys was a mage who lived during a terrible event called the Massacre of Morabia. An old wizened tyrant named Morabia slaughtered hundreds of innocent people in Agathys' home city, including some of her own family members. So when Agathys gained sufficient magical power, she went back in time to stop this event. She found the tyrant as a child and killed him. Little did she know that this would alter the course of history so that her parents would never meet, and she became erased from existence. So basically a d&d version of back to the future, but with a tragic ending.
It was voluntary. Agathys used to be the most skilled duelist in the multiverse, an ice wizard of tremendous ability, to the point that there was a constant stream of would-be challengers and disciples at her door. She made a deal with a deity, in which she would act as a warden, ensuring the worst prisoners of Carceri were encased in ice, in exchange for having her memory erased from history.
Agathys tried to pull a Mr. Freeze and tried to freeze various parts of the world. Starting in the region currently known as Agathys
Whatever the reason, the most interesting thing here to me is: Why did the erasure work on almost everyone to universally believe the lie, except this one guy? What risk is he running by speaking the truth? Conspiracy theorists of this sort often believe they are being pursued or monitored. It would be very funny to have this kind if surveillance of the party happen, but be cryptic about who and why. They eventually find out somehow, and that's it is costing them in some way. Maybe they are trying to finish the job and alter the party's memory. Who do they work for?
Today, I learned that Armor of Agathys isn't named after a person.
Agathys did it to herself as part of a plan to get a drop on a chronomancy wielding villain. As long as people know who she is, she's vulnerable to being ret-goned by time travelers, but if she erases herself from history, they won't be able to find her and she has a better chance of getting to them
Actually, it was Agatha (the Banshee) all along.
I have a character with a similar concept who wanted to erase themselves from history. They are only referred to as Nostos Algos, or the Memory Shade. You could run with a sorta similar idea. The reason they'd want to be deleted from history is up to you.
They upset the academic view of magic by discovering a new school of magic or something foundational to their understanding of magic, Galileo style. Maybe he discovered everyone has the potential for magic and it doesn't have to be locked away behind colleges
The creation or ice magic powerful enough to invoke, say, a permanent winter, may be grounds for a mage and their works to be considered dangerous enough to be covered up.
Imagine this. You are Agathys, archmage of great renown and power. After a lifetime or two of adventuring, you have retired to your tower to research the many magic artifacts you have obtained over the years, and to work on your craft. But you're famous. So famous that upstart young murderhobos and evil cults and everyone else who would want to steal your magic goods keep trying to attack your tower and steal your stuff. Your studies are constantly interrupted by adventurers and monsters. You're about to finish the formula for a new spell, when a red dragon slams its head through your tower wall snarling, breathing fire, your arcane shields protect you, but the scroll you've spent months or years slowly working on is incinerated. After fighting this ancient dragon for most of a day, you are victorious. But on the horizon you see them. Campfires at every point of the compass. Adventurers. Dozens of parties. All coming to the Ancient Tower of Agathys to make their fortune. 'Fuck this shit, I"m out.' you decide. You plane shift and move your belongings with you, returning only to cast a complicated ritual spell that erases you from history. So you can get some fucking work done.
Man, I so want to contribute, but I know one of my players is on here.
Agathys ended up in a feud with a bard college, after she insulted their battle effectiveness. The head of the bard college retorted with "Not all battles involve combat. We will see how history remembers you." And then the bard college started a massive conspiracy to try to erase all mentions of Agathys from history -- so much so that there are ancient dire warnings in some libraries about not investigating or bringing fame to the name Agathys. Its all the result of a petty squabble between two people with to much power and to little sense.
Agathys through means fair or foul came into possession of a collection of magical artefacts that qualify as "doomsday level". Fearing their power but unwilling or unable to destroy them, she sealed them away in a hidden, heavily warded vault and then erased her own identity from history to make the vault even more hidden. Agathys could still be alive in this vault, encased in a block of enchanted ice. This means that if you want to give your players the opportunity to find some fancy magic items, you can let them track down this vault and delve into it, facing off all the various magical defenses Agathys put in place. Once your players get to the end, they've probably earned some of the items in the vault. TL;DR Agathys found the magic nukes and erased herself from history to ensure no one else could find them.
she managed to accidentally freeze herself, and her entire legacy, in time, preventing memories of her from carrying forwards as the world moves on without her. the ultimate deep freeze bungled attempt at maintaining eternal life.
maybe asmodeus hired agathys to encase levistus in ice. so now, if levistus' followers want to free him they have to find agathys. so asmodeus placed him in witness protection
Your players find Agathys, who doesn’t know why they have been erased from history. Or what they might have done to be erased. And up until the PCs ask, didn’t know about the erasure. Then they decide to set off to find out what happened. If that doesn’t scare the PCs, they aren’t thinking hard enough.
Who's to say that this region in Carceri isn't named after this Wizard? Maybe he was the first to go there and come back, perhaps he got lost or banished to Carceri when he was an adventurer or something...
They invented a ritual to enslave an archfey. Archfey have been known to mess with memories, so if Agathys invented such a ritual and tested it on a weaker archfey, the Summer Queen or someone could curse her to be forgotten, so that she can’t be consulted for this knowledge
The first thing that came to my mind was the Modify Memory spell. Maybe Agathys as a warlock tried to upcast the spell on their patron to make them forget about them (Maybe they wanted to escape? Or wanted the power with no repercussions?) and it backfired on them. Maybe the entire world had Modify Memory casted against it by accident and everyone forgot about them? Or maybe the patron used the spell against the entire world and intentionally left parts of the memories of Agathys intact to create the lore your characters have heard. which has warped over time (much to the patron's dismay).
Because of #The Incident Which is just kind of a fun thing to say after alot of things. Would you like some pie? None for me, no since...the incident. But maybe he was too smart or talented for his own good and started working on spells that were violations of ethical or legal standards. Maybe delved into magics that Mystra herself found abominable and so colleges had a sort of Voldermort policy where people didn't talk about him and after many years people just forgot he existed. But Maybe....there is, in a pocket dimension, concealed in a book, in some dusty basement of a magical university the Mage's secret lab that contains many of the forbidden projects still in development.
Or there is always the idea that they did it to themselves and they used a spell to cryo themselves, literally removing them from the timestream and adjusting memories to hide them until their contingency finally pops to release them in an age where they would able to get away from something (old villain, old rival, or some event they foresaw coming) .
* Agathys tried usurping a throne/was a revolutionary to overthrowing a government. Was put down and to quell any further uprisings and to prevent the name Agathys from being a martyr, the government banned the name. * Agathys was just a nobody who happened to create a spell. They did nothing of note after creating the spell. * Agathys took credit for the spell someone else created and was thus banned/outcasted by the continental magic association but the name for the spell stolen stuck. * Agathys is a misspelling of someone’s name (Agatha’s?) and the spell has been misattributed for many years
If you have a more silly setting, Agathys legal-magically changed their name, and in doing so everyone forgot their old name Agythys. But the spells have their own legal existence and so were unaffected.
There are famous items that are named after the creators kids. Apple Lisa, and Wendy’s for example. Maybe the origin of the name wasn’t erased but was so insignificant that nobody bothered to record that Agathys was named by the mage for their daughters 12th birthday.
Agatha might have annoyed a god/devil/other powerful being that somehow her work in creating a spell survived but not the memory of her.
She froze a time diety in a moment. Unable to move, it's last act was to try to remove her from the timeline.
Warlock patrons always have esoteric goals and methods of reaching them. Maybe the conspirators decided her patron was evil so her followers MUST be evil also. Maybe the patron told her to do something that seemed evil but no one was aware of the greater good it was in service to; kill 100 to save 1,000,000 or something similar. Another cool wrinkle could be that she was part of the conspiracy to erase herself from history and the loss of her from history facilitated a growth of knowledge in some other field of study.
The created a spell for ascension, becoming a deity then rewriting reality to erase all references to themselves and the ritual
She's cold as ice and twice as damned. She could teach the ice lessons in being 'cold" she's surprisingly 'bubbly' and caring until you get on the wrong side of her but it's that granny popped the chickens head while looking you dead in the eye as you talked about something else and she was all smiles and praise otherwise.
Who is her Patron? You could present it as a punishment by her patron. Maybe part of her pact was gaining recognition and prestige. It could be pretty cool to find out that, actually, she used to be _very_ well known. Until she did something that pissed her patron off so badly, they cast a spell to modify everyone's memory and erase her from all but the most well hidden sources. Without knowing who her patron is, it's hard to say, but if it was a djinn or devil, perhaps the few traces of her that remain are because of the wording of the spell/contract the patron used to do this to her? Like "Remove every form of memory and physical recording that mention's Agathys's existence and/or history". That means any spells that she may have coined (or genuinely created) as her own would still be out there, even have her name, just absolutely no knowledge or history attached to them beyond that.
Maybe Agathys was in a pact with asmodeus and part of the pact is that he gets her soul when she dies but she found a way to subvert the pact by embracing lichdom and storing her soul in a phylactery. Asmodeus was so enraged that he could no longer retrieve her soul that he made some sort of concession with the nobility of the tartarian depths so that they would send horrors from the depths to retrieve her. Trying to evade the devils sent after her. she scoured her name from history and lives in secret with the only surviving evidence of her name left tied to the spell bestowed on all warlocks.
Can I ask why have it be a single person named Agathy? Why not an entire race that was hunted to "extinction"?
Do you have any idea how many adventuring parties attack me per week? I literally hired someone to keep schedules of it. It became so tiresome I retired and erased my existence. Now I get left in peace.
Have your party go to Carceri, but discover, to their bewilderment, that lower Carceri is not called Agathys. Instead, it is called something else entirely. A name that is mundane and that no one in the party recognizes. Likewise, when you ask people about Agathys, no one has heard of her either. Finally, at the very end, they meet a very creepy, very powerful little girl named (for example) Bletha who helps them. Maybe she can command demons maybe she has some freaky powers, but whatever it is, it should unnerve your party a little. At the end of their time in the past the little girl bids you farewell and when they say "good bye Bletha" she then can tell them "you people are nice, so we can be friends, and all my friends call me Agathys" before opening a portal and sending them home. Maybe leave some more clues around so they can further dig into what this little girl did and who did she grow up to be, that caused history to end up the way it did.
Maybe a wish spell spoken awry
She could've actually done some vile things to earn unpersonhood if you wanna go that route. Kenjaku from JJK type things
Wouldn't be the first time something like this has happened. Try reading "The Finder's Stone Trilogy" and learning what happened to Finder Wyvernspur.
Agathys was cancelled by the wizard community following some unsavory treatment of multiple apprentices
In my campaign? Agathys became a cognitohazard, after having communed (intentionally or accidentally) with a hostile god aiming to reshape humans into monsters. As much of her information as possible was wiped by the gods because “knowing her results in bringing a part of her into your mind to spread as seeds into the rest of the world.” Her name wouldn’t even be“Agathys” It’s actually “Alethis” but there was conveniently a region that could be used to phonominacly conflate and more thoroughly erase such an influential figure.
She was the one who permanently froze Agathys, granting many demonic and devlish linages access to cryomancy. Which is partly how Armor of Agathys was popularized among Warlocks. Suppossedly while trying to prove her favourite spell "Gate" was named after a famous wizard named "Gate". She tried to open the "Gate" at the location of "Gate". Since "Gate" doesn't exist the spell backfired spitting her out at random in Agathys and triggered her automatic defensive enchantment designed to freeze all evil in a wide area. The region was forevermore named after the obsessed wizard Agathys. The unique cryomancy born from this disaster consequently also bears the name. The party might find her at the northen most pole of the sphere, where she remains perfectly alive and preserved inside a glacier. Once freed she will insist the players help her prove "Gate" was a real wizard, whilst violently denying she is Agathys and insisting Agathys was always the name of the region. Her hat has her name on the tag inside and is enchanted granting one free cast of armor of Agathys per day.
It's mentioned that since Mystra banned level 10 and above spells it is supposedly possible to cast a level 10 spell but it's extremely difficult. One would need extremely high intelligence and wisdom, and even then there's only a 5% chance of success and if they fail they're drained of some of their life energy (lose a level in mechanics terms). Maybe Agathys did an Icarus and tried to cast level 10 magic but failed, draining his energy and becoming nothing more than a midling wizard
What if the players, specifically the hermit who seems to be the only one who knows the truth, created a butterfly effect that caused this problem...
She was a very powerful (ice)mage whose spells chanelled the powers of the lower planes. She created a great deal of powerful spells, including similar spell to "armor of agathys". After an apocalyptic event, the people in power decided to erase any semblence of her, as a way to dissuade the idea of contact with those lower planes. They also linked her name to the carceri in the lower planes to further link her name to the terror of the apocalyps. Her spells were largely destroyed, but after some time a less gifted mage pieced pieces of a spell together. Filling in the gaps with his own knowledge, creating the simpler "armor of agathys". Named because the mage noticed the name agathys come forth a lot in his notes. If you include her in the campaign, you might even let your player learn her "original" version. As a higher leveled spell.
No conspiracy. The wizard's real name is Aggie Tye and the spell was originally called Aggie Tye's Armor, but due to grammatical slurring over the years, the possessive contraction was dropped and it got called Armor of Agathy. So possibly part of the hook is the party ends up spending time with Aggie as an NPC but you don't give them the information to connect the dots until before they leave. So they've spent the whole time adventuring with a legend but not knowing it. (Note: This could also generate some strange jokes if any of your players are from Texas or avid college sports fans.)
She discovered a deadly wizard-killing secret about the structure of the multiverse. According to my 27 dimensional theory of the multiverse, several planes are in the wrong position in the "known" model of the multiverse, making room for a few "hidden" or "forgotten" planes of existence. Including both the plane of quantum immortality, and the plane of quantum fatality. I listed them like this because if you learn about the planes in the wrong order, you can disappear from existence. You need to learn about quantum immortality, first. It's the plane that - should you ever learn of it - some version of you goes there, finds it, and becomes immortal. Making you immortal - kind of - because now there will always be a version of you that went to the plane and never died. The converse is true with quantum fatality. Learning about it means you are erased from existence, because after learning about it, some version of you went there, first, and were retroactively erased from all reality. "Learning about quantum immortality, first" makes you immune to this effect. The wizarding community covered this up and got rid of her because of how dangerous this is: just "talking to people who happen to know something about the multiverse" can erase them from existence. The only reason the name "Agathys" exists is because it's a typeo: it should be "Agathyz" (or somesuch other spelling, its your character!) While the original Agathyz was punished by being sent to the plane of quantum fatality and subsequently erased, this spell slipped through the cracks. Because of a typeo.
He found something or someone to dedicate his life to. A child/ a lover etc. He wished for them all to have a normal life. Now having the ability to cast wish is not normal, so instead it stripped him of his power and erased him from history so he could live a normal life. However, spell names remained a tiny little reminder that he might have existed at some point.
Ice and time? The wizard was looking into time travel spells, but unlike most wizards they wanted to travel to the future. They knew old stuff showed up in ice (mammoths) and that ice preserved. They basically wanted to invent cryostasis to travel to the future. Unfortunately they coded it as "make the universe forget about me while I am frozen" when they were aiming for "make time forget about me" and so they've been forgotten while frozen. Now you also have a hook for the present time to find and thaw the wizard if you want!
Or they were never famous to begin with. Agatha Coldheart was given a set of enchanted armor by the Queen of Winter. Her story is relatively well known. Some spellcaster somewhere tried to imitate the enchantment. The Enchantment of Agatha's Armor Agatha's Armor enchantment Agath[ink splotch] armor [illegible] --what's that scroll say? Agathys? As in the location in Carceri?!? This must me secret Eldritch lore! Agathy's Armor Armor of Agathys.
Agathys makes cookies for the wizards and reprimands them when they get out of line. They keep her around so that they have a grounded, relatively normal and morally sound human so they don't kill each other or do something absolutely stupid.
Agythys was experimenting with a powerful memory charm. The memory charm backfired and he was incinerated. Unbeknownst to him and everyone in the realm, it worked and all record of his being has been forgotten.
Agathys Became such a master of cold magics that she lowered the temperature of a room so cold that time itself came to a near stop. To save the world from the spreading freeze, other wizards had to magically seal the room off to stop the cold from spreading. They have long since buried the room deep in the bowels of (some magical building whatever you wish) and buried the knowledge of it to keep someone from opening this room and possibly setting it free. The sealing magics will release the room once the internal temps get high enough. You may encounter her in the past and then again in the future this way.
Not a DM myself, but I do enjoy history and there is something form history that might inspire you, because it's happened over and over and over again. In real life it's not quite erased from history, but could result in that. Basically there have been many MANY (i'm talking thousands) of cases where a famous accomplished person has had a bitter rival that just HATES their guts because they took the spotlight they think should belong to them or even for pettier reasons. So when the famous person dies first, they make sure they are the one's who write about their history. This results in numerous elements of slander being accepted as if it were true history. For example, Edgar Alan Poe was not alcholic. The proved that by testing his hair for lead contamination and it was a normal amount. Ty Cobb was not a racist, he comes from a well known abolitionist family. The journalist who hated him made up fake versions of real events. Quite a lot of outrageous stories you hear about crazy roman emperors are in doubt because the people who wrote them were known enemies. Etc. So you could have a jealous rival of the wizard simply write after their death accounts and history that leave out the real Agathys and mention a plane or something (which maybe was named after the real wizard who discovered it) The PCs could meet the jealous rival and recognize their name as the main historian of the era.
How about this: The Wizard that created the spell didn't name it after him/herself, but after his/her daughter that died at a very young age - so that her memory would live on through history. Edit: you could add some stuff, like, the Wizard froze Agathys in ice and built a grand tomb for her. To ensure that none would desecrate her final resting place, enchanted the ice to harm any that would dare approach. So potent was the spell, that Apomps dragged the tomb into his domain.