Revenants are possessed undead.
They are the spirits of dead people bound into bodies and forced to obey the caster. Despite that, necromancers are hesitant to create such beings. Spirits that are brought in such a manner tend to come back changed, possibly insane or vengeful. This is likely the reason that makes them exceptionally hard to control.
While it hasn't been confirmed yet whether this goes for all Revenants, Fetohep is still in possession of a Class, however is incapable of levelling in it any longer, and kept having access to the Skills he had when he was still alive.
Powers and Abilities Edit
They retain the personality of their former selves, which makes them especially difficult to deal with opposed to the mindless Undead.