Or is there no such mechanic? Just heal and pray?
Kilran's snipe attack is not an actual one-shot, but it hits really
damned hard. I think the fight works such that you can LoS it, but it's hard since there's scant cover and a slowing effect if no one is in his melee range; I think as soon as someone can get close enough to slap him, though, he tends to stop sniping and the snare goes away. But it often is an over-zealous DPS that charges ahead, ignores the wave of adds in the back, gets aggro on Kilran, and gets too far from heals then dies and rages.