Eternal Death is an excellent undead to use because it possessed a passive skill called Aura of Death and Decay. In other words, it is a potent skill which combined the effects of Ainz's Despair Aura V and Despair Aura I, which made them capable of causing instant death and stat penalties to the enemy.
Furthermore, the stats penalty was not a mind-affecting ability. As a result, this allowed Eternal Death to bypass immunity to mind-affecting effects, which made it very hard to deal with. That said, if this ability were used under conditions where the friendly fire was enabled, it would swiftly paint a hellish picture of suffering and misery.
- Ainz requires two uses of Create High Tier Undead skill in order to summon it.