Ssthrass

"You will not enter the aqueducts! Lord Belial demands your blood!"

- Ssthrass, upon seeing the player

 the Sliverbolt is a Super Unique Serpent Magus found in the Dahlgur Oasis, just outside the entrance to the Ancient Waterway, guarding the passage.

He is a guaranteed spawn, even before and after his respective quest. He has Vortex, Electrified and Thunderstorm affixes.