The Skull of Corruption is a unique amulet in The Elder Scrolls II: Daggerfall. Using the Skull of Corruption on an opponent creates a duplicate of the victim. However, this duplicate will attack the original, not the wielder of the Skull.
When used, the skull will create a duplicate of the targetted enemy. This duplicate will then attack the original under the caster's will. The duplicate will then disappear once the enemy dies, or if the enemy manages to kill the duplicate. In most cases, the duplicate wins.
The Hero of Daggerfall must summon Vaermina on the 10th of Sun's Height to start the quest. After speaking to Vaermina, she appoints the Hero to a radiant dungeon to kill a Lich. Following that, she appoints the Hero to a radiant town in the region, where one will meet her worshipper and receive the skull.