Crucible - Kalis Ka Health Regen Ability?

I encountered (2 of us) Kalis Ka in the Crucible. The other person had died (under leveled) while I was cleaning out trash, and I was left with Kalis Ka. Not a problem as far as surviving is concerned, but his mana never went below 70% and he healed every 10 seconds or so. I could get him down below 50%, but his full (?) heal made it impossible to kill him. I looked at his abilities on the wiki, but I’m not sure what he’s using to heal. It’s not the spines or vomit, because he heals even if those don’t connect. I can’t find specifics on fury, but that’s all that’s left. And fury doesn’t sound like a heal ability. I could have sat there all day attacking and watching him heal over and over. Any ideas?

Might be due to Monster Mutators like Leeching or Regenerating.

Things like this may happen, if you lack DPS. There is mutator, that significantly boost HP regen, and mutator that provides life leech. And some enemies are capable of healing themselves - for example, Sentinel. If your DPS is too low, and LL/regen mutators happen, you may never kill him.
Just improve your DPS, and this problem will dissapear.