Tarthess

Tarthess, Descendant of the Ardanocs is a unique Barbed Lurker that can be found in the Occupied Ruins in Diablo III. It spawns only for the Resurrection event, where it tries to revive its demonic master.

In combat, it has the Poison Enchnanted and Fast affixes, the former being very deadly because the fight takes place on a very narrow bridge.

Killing Tarthess is required to complete the event, but the Resplendent Chest may be opened without killing it.

Trivia

 * This creature's title implies that it is the descendant of a demon, adding weight to Deckard Cain's suspicions that Barbed Lurkers are partially demonic creatures.