Immolith

An immolith is an undead demonic creature that is sometimes created when the spirits of deceased demons have fallen back into the Abyss.

Immoliths greatly despise living creatures, and they are often found accompanying other undead such as liches and vampires, although they can also be found with other demons such as horde ghouls, mezzodemons, and vrocks.

Immunity
Immoliths are immune to all disease, fire and poison.

Combat
Immoliths are perpetually surrounded by flames and foes getting too close are likely to catch fire. They attack with their claws, which can also cause foes to catch fire.

An immolith can curse enemies which slows them down and causes them to catch fire, and an immolith's grab can eliminate enemies' fire resistance. An immolith can heal itself and any nearby undead creatures.