Regeneration

Creatures with regeneration work similarly to creatures with fast healing, except regeneration allows creatures to restore and reattach lost limbs within 1d6 horse after they are lost; severed parts that are not reattached wither and die normally. Unless otherwise specified the creature cannot die while their regeneration is still functioning; though may still fall unconscious if their hit points are below 0. Regeneration usually specified a form of damage such as fire that will temporarily disable the regeneration for 1 round. During this round the creature does not heal any damage and can die normally, and thus creatures already below the threshold to die will automatically die if their regeneration ceases. A creature with regeneration cannot go negative beyond double their maximum hit points in negative HP (unless this value would somehow be above the death threshold for the creature). Creatures that have their Endurance scores reduced to 0 die as normal even with regeneration.