So after, chain-wiping in phase 3, I realized that it wasn't today that I would pull off 40K dps.
God, I just love ICC! Testing every ability the boss does, wiping, changing strategy... Understanding a boss is so fun! Human: 1 AI: 0.
So, the guide:
Phase 1 and 2: control puddle spawning (puddles grow up to a certain size).
So, you will need a side of the room clear for phase 3. I prefer the yellow side because 2 orange oozes: reset boss, 3 green oozes: death. Wich means you will need to make the green puddles spawn on the green side.
Now, your pet won't pull aggro from the green oozes if he is near the wall. Just FD as soon as the green oozes have cast their spell or they may move in aggro range of your pet.
In phase 2, never ever suffer a malleable goo.
Phase 3: Beware, at the start he may cast a last puddle. I believe there is a maximum number of puddles possible in the room.
Just tank him with your pet until he's at 6 stacks. Switch pets after making sure widow venom is active, and follow the wall (if you go in the middle, the orange oozes will aggro you). Continue until he gets dangerously close to the berserk. Then finish him before your pet gets at 9 stacks (like 100K/2seconds).