This is with regards to bosses with elemental "auras". The radius on their "aura" is so big it starts while the boss is off-screen. Even a ranged character can't attack without taking plenty of hits. Add to that the number of orbs in the aura that is circling which makes it impossible to avoid most of them. This mechanic is really aggravating.
Just fought a boss with both a rend aura and an electric aura AND haste. All I could do with my ranged character was drop turrets and mines and kite and hope he runs into them. Eventually, he died from this tactic but talk about a ridiculous and un-fun fight. I don't expect my ranged character to go toe-to-toe with a boss but I spent the entire fight keeping him off-screen so as not to get hit with his swarm of orbs.
And I did start the fight trying to stay close to him to keep away from the orbs but his AoE attacks plus the swarm of adds meant I had to keep dodging out of close range and right into his orbs.
This was on a mandate where I had to kill a number of bosses, most of which had these auras. The ones with a single aura was bad enough but there would sometimes be two of them together. Then there was this one with two auras. And after managing to get through all of that, the mandate was bugged as it kept showing 2 more bosses when there weren't any so ultimately I had to abandon it - which makes all of this even more aggravating and leading to this rant. :-/