You really gotta read the guide.
Acid rain from kaalut reverses your HP regen DRASTICALLY and will kill you in a second, like a poison that can't be resisted. The fence blocks it(look at how the rain is only falling on the left side of the video).
With knarst, I stood exactly there so I wouldnt pull adds and he'd come right back to me. You HAVE TO dodge tornado--it's OP on mobs too, and about to be nerfed. More details are here