Spectre

Spectres are incorporeal undead often mistaken for ghosts. They haunt the places where they died, retaining their sentience but now hating all living things.

Special abilities
A spectre has damage reduction 5/+1, turn resistance +2, and the usual undead immunities to critical hits, death magic, disease, level drain, ability drain, mind-affecting spells, paralysis, poison, and sneak attack. Furthermore, these monsters are incorporeal (which implies 50% concealment).

The attack of a wraith will drain 2 levels on-hit. In addition, a wraith can use an aura of unnatural once per day.