Sometimes, I see a whirling laser or some enemies chained together by some orange chain: those things kill a lot.
I don't know how much damage they cause, and I don't know what kind of move they pull out against me, but others seem to know that. How do I know? I've turned on every display in the options menu.
The affixes you're talking about are Fire Chain and Arcane enchanted. There's no way to tell the exact monster-level, but these two affixes only spawn in Nightmare and later difficulties (see this question for more information about the affixes).
Generally you want to stay out of the arcane "laser-beams" (and yes, they deal a lot of damage), which shouldn't be that hard, unless you're jailed or frozen. You can also break the fire-chains by luring a monster away from the others.
Fire Chain. Just look below the name of the monsters at the top of the screen, in the middle.
