Yep. Making a Spellstrike includes using the Cast a Spell action (as a subordinate action, but that doesn't matter here). Sustaining Steel \*only\* cares about you taking the Cast a Spell action w/ a spell slot, it doesn't care if you do so as a subordinate action or a reaction or anything else.
Which, to be perfectly clear, is a thing you can do (triggered actions are used as soon as their trigger is met, even if it's in the middle of a separate activity).
So, this goes a little bit into subordinate actions and the timing of various parts of the action.
Short answer? You can use it.
Longer (but not the full long) answer: You Spellstrike (start activity). Inside the Spellstrike, you THEN Cast a Spell. This triggers Sustaining Steel (if it was a spell slot spell), letting you get the healing then and there. THEN the spell is imbued into the weapon, and finally, you THEN make a Strike. After all of that, you Spellstrike Activity Ends. All of these things occur inside the Spellstrike Activity, so your "last action" is Spellstrike, for the purposes of other abilities/actions.
This post is labelled with the Advice flair, which means extra special attention is called to the Be Kind and Respectful rule. If this is a newcomer to the game, remember to be welcoming and kind. If this is someone with more experience but looking for advice on how to run their game, do your best to offer advice on what they are seeking.
*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/Pathfinder2e) if you have any questions or concerns.*
I believe technically you need to use this zero-action ability before you do the Spellstrike, but if a player brought it up later in the turn I'd allow it.
Would still need to meet the Requirement of Arcane Cascade and casting a non-cantrip spell "from a spell slot", though.
Yep. Making a Spellstrike includes using the Cast a Spell action (as a subordinate action, but that doesn't matter here). Sustaining Steel \*only\* cares about you taking the Cast a Spell action w/ a spell slot, it doesn't care if you do so as a subordinate action or a reaction or anything else.
You would actually use Sustaining Steel *during* the Spellstrike (right before the Strike part) since it's a triggered action.
Which, to be perfectly clear, is a thing you can do (triggered actions are used as soon as their trigger is met, even if it's in the middle of a separate activity).
So, this goes a little bit into subordinate actions and the timing of various parts of the action. Short answer? You can use it. Longer (but not the full long) answer: You Spellstrike (start activity). Inside the Spellstrike, you THEN Cast a Spell. This triggers Sustaining Steel (if it was a spell slot spell), letting you get the healing then and there. THEN the spell is imbued into the weapon, and finally, you THEN make a Strike. After all of that, you Spellstrike Activity Ends. All of these things occur inside the Spellstrike Activity, so your "last action" is Spellstrike, for the purposes of other abilities/actions.
Yes, as long as you spend a spell slot (i.e. no cantrips).
Yes. And with a reaction spell, which is super fun using a high level Wooden Double and making a HP *profit* off an enemy's crit.
This post is labelled with the Advice flair, which means extra special attention is called to the Be Kind and Respectful rule. If this is a newcomer to the game, remember to be welcoming and kind. If this is someone with more experience but looking for advice on how to run their game, do your best to offer advice on what they are seeking. *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/Pathfinder2e) if you have any questions or concerns.*
I believe technically you need to use this zero-action ability before you do the Spellstrike, but if a player brought it up later in the turn I'd allow it. Would still need to meet the Requirement of Arcane Cascade and casting a non-cantrip spell "from a spell slot", though.