Death and Buff spells.

[Mathius]

As a DM if I am running a monster that becomes a different monster at 0HP would buffs that effect the first monster effect the second form?

[keaton13]

Is this a monster that is in an official book? or is this a homebrew, I don't know of a monster like this off the top of my head, but if it's homebrew I think that would be up to you.

I think if it shifts from one creature to the next at 0hp without actually dieing then ya totally it keeps buffs unless it no longer qualifies for said buffs. Such as it starts out human with enlarge person on it, then it turns into a dog, enlarge person would no longer affect it.

But if it dies then sort of comes back as a different creature then no I would say no it doesn't.

Again if it's homebrew that is really up to you.

[Ashes]

Is this related to a certain encounter in the Curse of the Crimson Throne Adventure Path series?

[Fromper]

I know of one module that has a creature that dies, then another creature comes out of its body. In that case, the first creature is actually dead, and the second one is a new creature that was just gestating inside him. Thus, the first creature's buffs wouldn't apply to the second.

But I also don't know if that's what you were talking about.

[Claxon]

Is it just an affect like alter self or some other polymorph effect? If so, any buffs would continue, but the creature would most likely remain unconcious.

If the creature regains all its HP and is suddenly a new creature without any rules for how that happened, should the buffs persist? Probably not. But it's your game, and depending on how you want to run your table I think either way is probably valid.

[Mathius]

Actually this is from Carrion Crown.

Spoiler:

Wake the watcher encounter F14 Does the canker benefit from Bull's str, shield of faith, etc?