Bosses and Champions with it create duplicates of themselves, much as {{iw|Baal Baal}} did in Diablo II: Lord of Destruction. The clones have the same properties as the original, a big danger when the boss has nasty mods on top of the Doppleganger. Clones have only have half the hit points of the original, so the die fairly quickly, but they're not worth anything to kill, and while the player is busy with them, another Doppleganger or two are likely to appear.