Plagued and poison work, and will keep him from recovering, as his regen is decent, plus huge hp so the fight will take a while. Lightning weapons are a must for anyone in the front row/hitting melee. Harm works, lightning spells (including TKE) work. Enervation supposedly works, but didn't have to test it.
Not a boss kill, and drops only a journal explaining that the broken world gate is used for relics. Not really worth the effort, but a decent mob to train people with to work as a team effort for runs, like the lowbies/new players we have.