Regeneration

Description
Regeneration is a monster ability. Creatures with regeneration heal damage at a fixed rate, as with fast healing, but they cannot die as long as their regeneration is still functioning (although creatures with regeneration still fall unconscious when their hit points are below 0). Some types of attacks (noted in the creature's description) stop the regeneration on the round following the attack. During this round, the creature does not heal any damage and can die normally. For ex. Crag Linnorm's regeneration can be stopped by using a cold iron weapon.