Ooze Flood

First thing of note is the room. Every so often, an entire quadrant will be flooded with ooze, which of course hurts you and snares you.

Ooze will start flowing from the pipes there first before the flood, so can watch for that and get out of there. The 4 quadrants will be randomly filled, but each one must be filled at least once before re-randomizing.

So, the tank should tank Rotface in the center, the ooze won't reach the inner inner circle of the room. The raid can all stack up there too, in normal mode at least.

Slime Spray

The first major ability Rotface does is Slime Spray. This is where he randomly turns towards a raid member, starts a cast, then channels a frontal cone attack damaging all in its path.

The raid just has to move away from where he's facing to avoid as much of that extra unnecessary damage as possible. This is where stacking in the center for normal modes would benefit too, less distance to run if you can all just go through him to the other side.

Mutated Infection

This would be another major mechanic. What it does is puts a DoT on you, and the debuff also serves as a Mortal Strike effect. When it expires, or cleansed, it will spawn a small ooze which will be attacking you.

Little Ooze

Spawns when Mutated Infection is cleansed, and will be attacking you and spewing out a small damage aura. Let it, it won't hit that much, and has an immense threat lead so it won't go away until you die, or do some total aggro drop.

When 2 of the Little Oozes get together, they will merge to form a Big Ooze. Your goal is to take that ooze out of the raid so they do that.

Big Ooze

When 2 small oozes come together, they'll merge into a big one. These guys operate on a normal threat table and can be tanked, though shouldn't. They will hit very hard and should be kited around the room.

Can be kited by any class that can kite, hunters, locks, mages, etc. But likely, you'd want to stick with a tank class for that extra damage / hp buffer. Do ranged threat moves when possible, so obviously, some tanks are better than others for this task.

Meanwhile, people with the Little Ooze should drop theirs near the Big one so they merge with it. With each one merged, the Big Ooze gains a stacking buff that increases their damage by 20%. All the more reason to kite it around, and stay away due to the aura it has too.

Unstable Ooze Explosion

At 5 stacks (oozes merged), the Big Ooze will stop and do a cast and then explode. Sending 8-10 ooze missiles into the air in which they will land where the players are doing a lot of damage.

So the raid is to watch for that and move, it's like a Shadow Crash, it'll hit the location you were at when targeted. So if the raid was mostly all in the center, that's where all the missiles will hit, get out of there.

And that's basically the cycle of the whole fight. Avoid slime spray, get Mutated Infection, take the little oozes out to big ooze, kite the big ooze, avoid the explosion, repeat til dead. Except, the rate of Mutated Infection will increase as the fight goes along, so things can get hectic at the end.

Hard Mode Summary:

More damage, more HP, and Professor Putricide joins the fight from the balcony performing...

Vile Gas: This is similar to the Festergut one, but not as lethal. What it does is roots you for a second or two, you can still cast it and all. And it still hurts people around you. The adjustment the raid has to make is to keep the minimum amount of ranged at ranged (3 / 7) and spread out so it's not cast on the melee pile.

Otherwise it's the same fight, this is a relatively easy Hard Mode, comparatively.