In order to skip two burrows (the bare minimum, just as a possibility), and assuming you double his four second cast to eight seconds, you'd have to take just over half of his health in eight seconds. DPS him down to 75%, let him burrow, kill two adds, then DPS him to 50.5%, and hit everything you have. He has to die, because if he burrows, there's no chance.
512,278 HP x 50.0001% = 256,140 HP
256,140 / 8 =
32017.5 DPS
Your group needs to pull 32,017.5 DPS absolute minimum for 8 seconds. Realistically you won't have 8 seconds, though, because you'll have to react to him casting the spell, and it's likely that some of those 8 seconds will be taking up by GCDs hitting the cooldowns (Bloodlust, Avenging Wrath, TBW, etc.).
I'm not saying it's impossible, I mean heck, if somebody did it, they did it. It just doesn't look feasible to me.
EDIT: And it appears to be a common idea to post on WoWhead and tell others that you "brute forced" things, or that the only way to do things is to "brute force" them.
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Moduspwnens - Shattered Hand
