Basically the hardest, optional fight in the game. Every other enemy in Arx dies way quicker (even the end times fight).
Hungers Mark from the Devourer Armor Set provides a Mark on a random enemy. If the enemy dies, you get a free refresh of all your skills (free second skin graft without cost).
The Devourer Set is by far the best set in the game. It's really sad, that INT or FIN based builds didn't get something similar.