So, I know this thread is tagged “D&D General”, but it got me thinking about how my homebrew system would handle it. It aims for compatibility with B/X monsters and adventures, so I guess that makes it kind of adjacent even though it’s mechanically quite different.The fighter's friend is hurt, even dying. The fighter prays to the gods to heal their friend. How is this action resolved? If it's a Religion or similar sort of check, what's the DC?
You roll 2d6 + attribute + rank to use trained skills and specialties. I’m leaning towards allowing them untrained at 1d6 + attribute. Since spells are just another specialty, and everyone (except barbarians) has magic points (mp), the fighter could spend the map and attempt to cast Cure by rolling 1d6 + Piety (the casting attribute for divine spells).
I’m still working on a revision, so I’m not 100% on how the casting roll will interact with Cure, but assuming 1d6 is unlikely to generate an adequate result, the fighter can gain more dice by making sacrifices*. It doesn’t have to be a literal sacrifice. Taking on an obligation or service to a deity would be reasonable to gain at least +1d6.
So thanks @pemerton for the thought-provoking post!

* You can give up something to gain +1d6. You can gain another +1d6 if it’s large or high quality (or an additional +2d6 if it’s both). You can also trade on your reputation in this way, but that risks generating infamy as a complication.