Ssthrass, The Silverbolt is a Superunique Serpent Magus that stands between the exit at the north of the Dahlgur Oasis and the Ancient Waterway in the Blood and Sand quest.
Ssthrass features in The Devil's Hand quest/event as detailed in game files extracted from the PTR of Reaper of Souls. He drops Dark Coven Scroll of Illusions.