So I've noticed something interesting about this when I was farming Hatebringers, and should've posted here. When you come out into his room, make sure you kill all the trash on the way to his platform (including the pack you can skip when you first enter), and it will trigger him to walk up out of the water and up the ramp to his platform. *LET HIM GET ALL THE WAY UP THERE* and he'll drop his loot much more frequently.
I kid you not, I had *50* kills of him down near the edge of the water, and got a neck like twice, no other loot. One time I afk'd for a minute after clearing the trash and so he made his way up to his platform - guess what? Hatebringer. I noticed the difference, and so started doing this to farm, guess what? 2nd Hatebringer in 5 more kills (and more consistent loot in general).