Found out yesterday that using Nullification on Zantarin when he is “charging” his sHoTgUn sPeLL oF dOOm cancels it. Pretty handy especially in the Crucible. I thought I should let you know. 
using nullification on his is handy anytime for the “reduced elemental damage” portion of it, too.
Nullification proving again that is one of the best abilities in the game.
Also possible with the devotion skill “cleansing waters” i assume?
Which button do I press to stop Kuba from healing?
It’s so good that I had it on 10/10 in a BWC sorc and it’s so worth it in 150-170 crucible.
G into quit, I guess? On a serious note, do items with reduced health regen effects also reduce his healing?
AFAIK nope, it’s not normal regen, the pool is basically a wendigo totem.
Well, he only deals acid and vitality damage. 
To test, but it should work. They probably share the same skill template.
Yeah it’s OP, if you stand in a blood pool taking no damage thanks to Mirror it still heals him… I would prefer if the pools had life steal.