This is arguably a better fight than Rotface (if not quite as much fun) with loads going on. There are three phases, though only phase three is markedly different. Phase one has a tank hold onto the boss while everyone gives him hell. Someone else (probably another tank) will drink something silly and turn into an abomination. They'll be guzzling up the slime patches on the floor, and spitting on the oozes... I should mention those things I guess.
There are patches of slime on the floor, don't stand in them. You knew that already didn't you.
Oozes, these form from the green and orange vats to the left and right. We find it best to keep the raid by the green vat but positioning is up to your raid leader. When the green ooze spawns you need to kill it fast. It will pin someone to the spot and slowly move towards them before doing a damaging knock-back. This damage needs to be split between several people, so go stand on the person it pins (DBM marks them). The orange ooze targets someone and chases them, if it's you then just kite the thing about. As long as your abomination driver has slowed it this will be easy and you can throw curses and whatnot over your shoulder as you go. If it doesn't target you then you need to kill it. It changes target every 20 seconds or so and does a lot of damage when it catches someone, so melee tend to stay away -- it's up to us ranged bods to do the business here.
Destro locks will appreciate their burst damage on these slime things but all casters will appreciate the ISB debuff from afflocks and demo. Affliction has more chance to keep damage on the boss while killing the ooze but don't hold back on it, the boss can wait, that ooze needs to die quickly. Also, if you are demo, remember to not only start with a Shadow Bolt but make sure you trigger the Decimation buff as the slime dies so you can use it on the boss (remember it's a duration effect now).
That's about all you need to worry about in phase one. Manage that and get the boss to 80% health. Then he stuns everything for a bit while he fixes himself a drink, grows some tentacles and removes the stun effect. Thus starts phase two.
This is the same as phase one but with two extra things to watch out for. First is a couple of flasks of gas that he puts on the floor, these explode so don't get near them. The other is Malleable Goo, he throws this about the room so keep an eye out for it and move if it heads your way. The goo does splash-damage too, so move a good way.
Keep that up, destroying oozes, dodging slime etc, until the boss reaches 35% and then you get to phase three. Again, he nips off and has a drink of something dodgy and comes back somewhat stronger.
This is a burn phase, the abomination guy will now be out and so the slime puddles will start to cover the floor (remember Vashj?) and there's a really cool mechanic on the tanks that you don't need to worry about ("yar-boo" to the healers again). Keep dodging the goo and avoiding the flasks, don't stand in the slime puddles and nuke the hell out of the boss. It's a good idea to stand near the edge of the slime puddles so that there is more overlap if you get targeted with a new one but be aware that these things expand so keep moving. Also, don't stand in the kite path of the tanks, just follow along behind.
The burn phase will be ideal for demo and afflocks, where you may have lacked some of the burst damage of destro on those slimes you can now really bring the pain, especially as Bloodlust/Heroism will probably be saved for this phase.
Blood Pact is a weekly column detailing DoTs, demons, and all the dastardly deeds done by Warlocks. If you're curious about what's new with Locks since the last patch, check out WoW.com's guide to patch 3.3 or find out what's upcoming in Cataclysm from the BlizzCon 2009: Class Discussion Panel.