Sabnock the Infector, Marquis of Decay, is a Unique Enslaved Nightmare found in the Besieged Tower Level 1 in Act IV of Diablo III, added in Patch 2.2.0. He may be nominated a bounty target.
In combat, he has Orbiter, Desecrator, Plagued, Teleporter and Fast affixes. In addition, he can summon other demons (mostly Armored Destroyers). Both Sabnock and his minions have triple attack speed.