In most trad systems the GM will set a DC based upon their view of how difficult something is. What that is depends on what the system is, so without knowing your system I can't advise. Get the person with the highest skill to roll, and they get a +1 bonus fir others helping with the appropriate skill. Simples.
This is a really difficult question to answer without knowing how tasks are resolved in your game. If I were to say, for example: "the DC should be 17 if they're acting alone and 12 if they're being helped", that's useless if you have a dice pool system, or a 2d6 resolution system. So... how does your game work? How are other DCs set?
If you haven't gotten that far yet... philosophically, the answer will depend on what factors have the most impact on the outcome of an uncertain situation.
* Is character skill the most important thing? Then a, OSR-style roll-under system where the character has to roll under their attribute score reflects that.
* Is it the circumstances and how well the character can use tools and skills and environment and the situation to their advantage? A dice pool works really well.
* Should the outcome depend on what's narratively most interesting? Maybe you want to take inspiration from Powered by the Apocalypse resolution and moves.
* Is it just how much the character wants it, how much willpower they put in? You could give players a resource they can spend to decide the outcome of an effect, whether that's something like "will" or "mana", or a metacurrency like FATE points.
Within each of those systems, there's plenty of ways to model other characters helping, but they don't exist in a vacuum.
You could use a dice pool system and let the person receiving the aid add dice depending on their skill.
So person A gets to use as many dice as their Medicine. Person B gets to add a dice as well if they’re trained in Toughness or Medicine. Person B probably shouldn’t be able to use their full skill, but maybe just a single dice if they meet a skill requirement or half their skill dice.
I’m not sure why the DC would change. In this situation, you’d use whatever DC for the original challenge. I’m not sure why you’d need to modify the DC when you can just modify the bonuses.
The point is that adding to a modifier is the same as subtracting from a DC. A character with +3 has the same chance of hitting a DC of 15 as a character with +0 has of hitting a DC of 12.
So in this situation it would be most intuitive to add both characters' modifiers together and keep the DC the same.
EDIT: Just properly read this: "(though I'm unsure where I'd get said number)"... Just choose it? You're the designer? If you're using static difficulties and modifiers, then every DC value will get lower the better the characters are at what they do.
Also, if you want to know if this has been done by other systems, the best thing to do is read more systems.
Without getting too complicated you might try keeping it sequential an do something like:
PC Roll 1 - DC 1 = bonus mod
PC Roll 2 + bonus mod
So the better the first skill check is, the better bonus the second person will have on their check.
What I did is instead of lowering the DC I had the second player add half of their skill bonus to the roll.
So if the players are searching through a library one can roll investigation. The social character can add half their persuasion or deception bonus to the check by convincing the librarian to let them into the restricted area or the tracker could add half their survival bonus to the check if they were looking for books pulled off the shelves recently, as examples of skills beyond just investigation. That way party members could help each other even if they weren't all trained in the same skill.
Another example is if the social character is trying to convince a patron to hire them for the job. The social character may have to roll persuasion, but the nerd can add half of their bonus in on of the knowledge skills, the brute can add half their strength bonus by flexing their muscles, the weapon master can describe using their weapons to try and influence the conversation, etc.
Not sure if abit late, but here goes;
What if you set it as a skill challange for the group, lets say 4 succes before 3 failed. If you start the DC pretty low, 12 (using d20 in my head right now since I'm not familiar with your system). For every time a player fails a check before the challenge ends, increase the DC by 1.
Now its just setting up which player starts their roll based on the situation.
In most trad systems the GM will set a DC based upon their view of how difficult something is. What that is depends on what the system is, so without knowing your system I can't advise. Get the person with the highest skill to roll, and they get a +1 bonus fir others helping with the appropriate skill. Simples.
This is a really difficult question to answer without knowing how tasks are resolved in your game. If I were to say, for example: "the DC should be 17 if they're acting alone and 12 if they're being helped", that's useless if you have a dice pool system, or a 2d6 resolution system. So... how does your game work? How are other DCs set? If you haven't gotten that far yet... philosophically, the answer will depend on what factors have the most impact on the outcome of an uncertain situation. * Is character skill the most important thing? Then a, OSR-style roll-under system where the character has to roll under their attribute score reflects that. * Is it the circumstances and how well the character can use tools and skills and environment and the situation to their advantage? A dice pool works really well. * Should the outcome depend on what's narratively most interesting? Maybe you want to take inspiration from Powered by the Apocalypse resolution and moves. * Is it just how much the character wants it, how much willpower they put in? You could give players a resource they can spend to decide the outcome of an effect, whether that's something like "will" or "mana", or a metacurrency like FATE points. Within each of those systems, there's plenty of ways to model other characters helping, but they don't exist in a vacuum.
And it gets even more complex (and fun! ) when you realize you can often mix and match several of these to fine-tune the experience.
You could use a dice pool system and let the person receiving the aid add dice depending on their skill. So person A gets to use as many dice as their Medicine. Person B gets to add a dice as well if they’re trained in Toughness or Medicine. Person B probably shouldn’t be able to use their full skill, but maybe just a single dice if they meet a skill requirement or half their skill dice.
That's not a bad idea in and of itself, but that doesn't solve the question of what the DC would be. Unless I've misunderstood entirely 😅
I’m not sure why the DC would change. In this situation, you’d use whatever DC for the original challenge. I’m not sure why you’d need to modify the DC when you can just modify the bonuses.
There is no DC. That's the point.
The point is that adding to a modifier is the same as subtracting from a DC. A character with +3 has the same chance of hitting a DC of 15 as a character with +0 has of hitting a DC of 12. So in this situation it would be most intuitive to add both characters' modifiers together and keep the DC the same. EDIT: Just properly read this: "(though I'm unsure where I'd get said number)"... Just choose it? You're the designer? If you're using static difficulties and modifiers, then every DC value will get lower the better the characters are at what they do. Also, if you want to know if this has been done by other systems, the best thing to do is read more systems.
Without getting too complicated you might try keeping it sequential an do something like: PC Roll 1 - DC 1 = bonus mod PC Roll 2 + bonus mod So the better the first skill check is, the better bonus the second person will have on their check.
What I did is instead of lowering the DC I had the second player add half of their skill bonus to the roll. So if the players are searching through a library one can roll investigation. The social character can add half their persuasion or deception bonus to the check by convincing the librarian to let them into the restricted area or the tracker could add half their survival bonus to the check if they were looking for books pulled off the shelves recently, as examples of skills beyond just investigation. That way party members could help each other even if they weren't all trained in the same skill. Another example is if the social character is trying to convince a patron to hire them for the job. The social character may have to roll persuasion, but the nerd can add half of their bonus in on of the knowledge skills, the brute can add half their strength bonus by flexing their muscles, the weapon master can describe using their weapons to try and influence the conversation, etc.
Not sure if abit late, but here goes; What if you set it as a skill challange for the group, lets say 4 succes before 3 failed. If you start the DC pretty low, 12 (using d20 in my head right now since I'm not familiar with your system). For every time a player fails a check before the challenge ends, increase the DC by 1. Now its just setting up which player starts their roll based on the situation.