A yurei is a ghost which died in a horrible way and has unbridled resentment for the living. It is defined by both its thirst for vengeance and its willfulness to wreak its malice on any creature it comes across. Resolving its underlying issue that spawned its resentment can put a yurei to rest, but the passage of time can make such efforts impossible.
Undead Nature. A yurei doesn’t require air, food, drink, or sleep.
Creature of Spirit. A yurei can’t be polymorphed against its will.