Mythic: Chronomatic Anomaly

For those gunning for this achievement at 120 and beyond, it's very easily soloable. You have to ignore a particular mechanic though!

As the boss beats on you, you will gain stacks of [spell=206607]. At 10 stacks, you instantly DIE...no matter what level you are.
To avoid this happening, it's fairly straightforward - just DPS the boss! When he starts channeling [spell=219823], you would normally kill some adds, get an orb, and interrupt him. DON'T do that! The damage from [spell=219823] is negligible at 120, so just keep DPSing the boss until he is dead.