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.
Yep, not complete one-shot (tough I've seen horribly geared players get one-shotted) but combined with adds fatal for many group. I like tactic where whole group moves to next pillar together (so he can snipe only one) and if we are lucky target am I because I can use Force Speed to avoid it in time, or whoever Sage/Shadow can. Sentinels can use Force Camo