Introduction
Rotface is one of the two abomination bosses in the Plagueworks section of Icecrown Citadel that players need to defeat in order to unlock Professor Putricide's laboratory and fight him there. Rotface uses ooze-based abilities.
Tactics
Rotface is a fight similar to Grobbulus in some ways. Ooze adds, hurting ooze puddles on the ground, kiting of the boss - that kind of stuff. You will need at least 2 tanks for this - one for the boss, one for the adds.
The boss tank should start the fight engaging Rotface and keeping him in the center of the room. Melee, healers, and all casters should run in and stay right behind the boss, within his hitbox. Hunters should be at their minimum range, to the sides. The add tank should go somewhere to the outskirts of the room and wait for the adds to start coming. A paladin or a death knight might be better than warriors and druids because of the wider array of ranged attacks.
The first distinct feature of the fight are the ooze floods. There are four areas that might be flooded - south-west, south-east, north-west, and north-east. Floods will cover roughly 1/4 of the room, never reaching the middle of the room where everybody but the add tank is. They will also happen semi-randomly - the floods will go through cycles, each area being flooded exactly once per cycle. So if NW is the first flood, the second one will happen in either NE, SW, or SE. Let's say it's NE. Then the third one will be either SW or SE. Let's say it's SE. This guarantees that the fourth one will be in the SW. Then the cycle resets - identically to the Twin Val'kyr in ToC and their four special abilities.
The next thing to watch out for is the Slime Spray. Rotface will target a random raid member and being the 1.5 second cast of Slime Spray (during those 1.5 seconds the boss will follow his target). After the cast is over, Rotface will channel the spray for 5 seconds, inflicting damage every second. There are few ways to deal with this: You can have the targeted person swap places with the tank. This way only the target (note that the targeted person can run back to the group as soon as the channel starts, effectively taking no more than 1-2 ticks) and possibly the tank will get hit. However if the person is not quick enough, Rotface will being his channel under an angle that might hit more raiders. The alternative is have everybody who is not being targeted run to the tank as soon as Rotface picks a target - a raid warning will announce it. This way no raider should take more than 1-2 ticks, and even that will depend on their own reaction time, not the target's. Of course, it is also risky.
The third and last aspect of the fight are the oozes spawned through Mutated Infection. Every so often Rotface will target a random raider and debuff them with removable Mutated Infection. The infection will last 12 seconds or until removed (it's a disease), and will spawn a Small Ooze. It doesn't do much damage, but is not tauntable and starts with huge lead in threat. This means that the Small Oozes will stay with the person who spawned them until they merge with another ooze. If there are no Big Oozes, have the newly infected person stay with the add tank until another Mutated Infection is cast, and another Small Ooze spawns. The two small oozes will merge and form a Big Ooze, which will follow normal threat rules (but is still not tauntable). The add tank should kite the Big Ooze in a circle around the room, avoiding floods and the Sticky Ooze puddles the Big and Small Oozes shoot at him/her. Every time there is a Mutated Infection, the player with it should run between the tank and the Big Ooze, drop its Small Ooze there, wait for the Small Ooze to be absorbed, and only then return to the middle. Tanks, the Big Oozes are not tankable, their damage is too high. Kite them!
So the first two Small Oozes that merge will form a Big Ooze. Every next Small Ooze that merges with the big one will add a stack to its Unstable Ooze. When that stack reaches 5 (after the 6th ooze has spawned), the Big Ooze will freeze in place and cast Unstable Ooze Explosion. As soon as the cast is over, everybody should scatter to avoid the flying ooze missiles. Don't forget to avoid the ooze floods, and make sure to stack back in the middle as soon as you can. Note that if two Big Oozes merge, they will "cancel" each other - both will just die. Utilizing this should make both the fight and the achievement associated with it easier.