Unholy Armor

In Warcraft I
This ritual invokes the recipient with a mystic armor of invulnerability. Weapons will have their effects dissipated when striking the wearer. This armor is constructed from the souls of the damned, and they absorb the pain that any blows would normally inflict upon the wearer. The price that is exacted from those who are bestowed with this invulnerability is a high one, however, for they must sacrifice a portion of their soul to act as a magnet to bind these lost souls to themselves. After some time, this binding will weaken, and those who make up the armor will be released back into their eternal torment.

In Warcraft II
This ancient Necromantic spell transforms a portion of the recipient's life force into an unearthly, phantasmal suit of armor. This spectral armor then absorbs the damage from any attack directed at its wearer for a limited amount of time. As the magiks that link this armor to its host cease, so will the invulnerability that it grants.

In Warcraft III
Unholy armor was a generic armor type for the undead that was upgraded at the Graveyard building.

World of Warcraft
Ancient Shadowmoon Spirit used the spell to absorb damage.