Dark Sun - Destiny and sacrifice
An athasian wraith is a non-corporeal undead capable of moving freely between the gray and the land of the living. It can possess unliving objects of all sorts as well as unintelligent creatures such as insects. When not possessing an object, the wraith appears only as a green mass of churning darkness.
When a wraith attacks, its form passes through the target and a feeling of icy chill passes through the person, the cold stealing his strength.
A wraith can also reach into a creature and grip its heart. A person held in this way cannot move, and the wraith can read surface thoughts as well as feel if the person is lying.
To remain in the land if the living, a wraith must anchor itself to an object. Destroying that object is the only way to permanently destroy a wraith.