The Tavern

Minor internal consistency issue:

Ignite Blood demonspawn mutation causes enemy blood to burst into flame when cut.
Hydras have blood, and bleed when cut.
This triggers ignite blood, as one would expect.
Cutting off a hydra head with a fire brand cauterizes the wound, preventing new heads from growing in its place.

Logically, then, it follows from these interactions that igniting hydra blood by cutting off a head would likewise cauterize the wound and prevent head growth, but this does not happen. So, this sets up players to expect to be able to decapitate hydras when they have Ignite Blood and a slashing weapon, only to be in for a very unpleasant surprise when they realize they can't.

I suppose, similarly, one would expect a hydra engulfed in flame might experience the cauterizing effect as well, though it makes more sense that it might not, because in this scenario the fire isn't originating from the decapitation wound like it is in the Ignite Blood scenario.

To cauterize a wound, you have to burn the *flesh* which was wounded. Ignite blood just ignites the blood as has left the body (otherwise you'd be able to just nuke their blood without having to hit them first).

Relatedly: should hydras auto-cauterize if they're standing in a cloud of flame, or are currently burning from sticky flame?

But, when blood leaves a body, it's abnormal for it to not have contact with the flesh at the point of exit. Pretty much the only case I can think of would be when it's extracted with a syringe.

But it could ignite only after it leaves the body. (Otherwise it would be effectively a universal passive sticky flame, which it's not.)