Abyssism

Raises to life every demon that has ever fallen in battle while in the Abyss, restoring them as skeletons to full hit points. The skeletons are under the casters control, the spell ends once every skeleton is killed. These skeletons have knowledge of exactly who killed them and will do everything in their power to have their revenge upon them or their descendants, the caster of the spell must, however, grant them permission to do so first. (This spell is a work in progress, if it's too OP than perhaps your DM should a small group of dead demons).