Vile Sentinel, Pestilent Infector is a Super Unique Toxic Construct that can spawn in the Realm of Shadow in Diablo III. Either two of the four elemental Sentinels will guard the body of Zoltun Kulle, appearing when players approach. Killing them is not mandatory, though.
Vile Sentinel has Teleporter, Reflects Damage and Poison Enchanted affixes in combat.