Primeval Thressia

Overview

Primeval Thressia, Font of Blight is a secret Taken boss. Defeating it is the last step of the Buried Bloodline catalyst quest. It sits at the bottom of the double-helix stairs before the last boss, reached through the Toland orb portal.

Fight

Thressia starts immune to damage. Clear the room, then use the torches and totems around the Ahamkara skull, which follow a logical order. Activate the correct totems to drop the shield, then deal as much damage as you can before the buff ends. Repeat as needed. The catalyst's perk, Splitvein Lineage, weakens a weapon on hit while Devour is active.