I went with affliction and gosup. I tried out several things and for me it worked the best to gather 4 mutations and just spam sb+ss on as many adds as possible. If you run out of shards, finish one with DS and continue dotting. I used the fel imp (target switching) and put him on assist, so he attacks the blobs with me because he does reduced damage to the boss all the time (he doesnt benefit from your mutated buff). When you have burn phases on the boss you just gather your 5th stack and pop CD's. This of course depends on your strategy, but it is definitely beneficial to assign WL's on add duty if you want to kill them (in the burn phases we let the boss soak 2-3 waves). Also, the Infernal is better on this fight, because the doomguard also doesnt benefit from your mutated buff and the onfernal does some good aoe dps on the blobs.