For the Festergut and Rotface fights, pay attention to the ground textures. There's an outer circle at about 30 yards from the edge of the boss's hitbox. You can stand on that circle at the pull and get your rotation set up. Then, there's an inner circle, with spiky triangles and shit. If you drew lines E/W and N/S through the center of the room, they would intersect the inner circle at the same place as one of the triangle spiky bits every time. These points are good to know, as you will see.
Festergut
Regular Festergut is just a DPS race with a little movement for the spores and some DPS damage mitigation management. It's pretty fucking easy to DPS. The main trick in all cases is to use your Shadow Ward to mitigate the Pungent Blight and save yourself the bother of taking 3 stacks of Inoculated. <Insight> have one spore called to go to the tanks, ranged are left to figure out whether it's faster to run to a tank spore or a ranged spore and GTFO the middle a.s.a.p. Warlocks in general are good choices for staying out, thanks to the teleport circle, but also good choices for stacking on the tanks.Affliction: Start your rotation from the outer circle. If pulled by a tank who isn't a halfwit, Festergut should start in the middle and stay there, and you can cast everything you need from the edge without having Grim Reach. Use the instant GCDs of your startup rotation to move towards the outer rim of the inner circle and drop your teleport there. Stay outside the inner circle, so you remain a target for vile gas. If you are ranged-heavy, an affliction warlock is an excellent choice to stand on the tanks and never, ever, ever move. Otherwise, get at most two stacks of Inoculated, teleport back to your casting spot, and use Shadow Ward before Festergut expels his Pungent Blight, and you'll be fine.
Demonology: Same deal as Affliction. Again, if you've got a ton of ranged, Demonology warlocks are excellent choices for stacking with the tanks, since immolation aura is a respectable DPS chunk. Again, Shadow Ward with two stacks, or Shadow Ward + Metamorphosis with one stack, and you'll be fine.
Festergut - Heroic
The added fun mechanic here is everyone's favourite: Malleable Goo, which Professor Putricide lobs from his balcony in the NW of the room. This makes standing towards the SE preferable, to give yourself more time to avoid the goo. Unlike the actual Putricide fight, in H-Festergut, the incoming goo puts a green circle under its landing point, which is convenient. The range on the explosion is 10 yards, though, so you do have to move quickly.Unlike normal mode, where lurking near the middle, but in range for Vile Gas is good, on Heroic, being as spread out as possible towards the edge is preferable. Drop your teleport circle, before the pull, on the outer circle on the floor, and then move 10 yards to the side of it. The Circle masks the goo puddle, which would be a huge pain in the balls if you weren't going to just use the 'port to get out of it. Make sure no mouth-breathers in your raid are standing on your circle. Leave the inner circle rim for healers.
You can survive with 2 stacks of Inoculation, Shadow Ward, and a quick Death Coil right after Pungent Blight to help make up the health deficit. Whether you should or not, is up to you. If you die, you're the moron, not your healers. Remember that Vile Gas can come just before Pungent Blight, so you might want to make sure you're human and have EMFH on CD for that conjunction.
Rotface
Normal-mode Rotface, <Insight> puts everyone just outside his hitbox, we soak the slime spray, let a Big Ooze form first in the middle and then run little oozes to it until it explodes. Rinse, repeat. You might as well drop the port for getting back to the middle after running an ooze, or moving out of the ooze explosion.Affliction: The main thing here is not to neglect the ability of an interrupted Drain Life / Drain Soul to refresh your corruption while you're on the move. This is especially important if you're using the NMIC ab initio, and rolling crit.
Demonology: Yay, you get to be in melee range. Don't forget Immolation Aura, and don't forget that you have Demon Charge if you need it to get to or from the boss, as well as your circle.
Rotface - Heroic
Heroic Rotface adds Vile Gas to the mix. Unlike Festergut's gas, Rotface won't disorient you, but it will chain, and it hurts a lot, so you can't stack all the ranged in the middle (or everyone will die in a hurry). This makes the floor pattern very important.You remember I mentioned those spots on the outer rim of the inner circle at the cardinal directions? Those four points are the points of least movement. Although graphically the slime that comes from the walls looks like it is lapping at your feet, on those four magic points, you are just outside the border of two pools, and you're eligible for ranged vile gas. Drop your circle on one of those points, and let no man, dwarf, gnome, goat or night fairy take it from you.
Edit: I added a picture! Click for legible version.
Shadow Ward is again useful because the Big Ooze's aura deals shadow damage and will get kited past your jealously-guarded spot. Either move (sacrilege!) or use Shadow Ward and Death Coil.
Professor Putricide
Depending on how your raid handles this fight, your teleport can be a great tool here, because you can use it while targeted by the Volatile Ooze, giving the raid more DPS time on the ooze. Use it as late as possible.Affliction: This fight is kind of balls for Affliction. It's almost impossible to roll corruption on the Professor, so replace NMIC with your back-up trinket (which you have right? right?) and deal. Each ooze/cloud should get a full cycle of dots on it. Make sure to put full dots up on PP before the Tear Gas transition. Overwrite if you have to, it will be a DPS gain.
If your raid DPS is high enough, dot up the add, then switch back to PP. You'll be doing respectable damage to both. Avoid getting yelled at by the raid leader.
Demonology: Do your damnedest to trigger Decimation from the ooze/cloud and use it on the Professor. Don't forget immolation aura for damaging the adds as they pass by, and Demon Charge to stay in range.
Professor Putricide - Heroic
Heroic mode adds Unbound Plague to the encounter and replaces the Tear Gas phase transition with a sly two girls, one cup reference. Nasty. The sheer RNG of Phase 2 with the plague, malleable goo, flasks and beefier adds makes this fight… unpleasant. Like many guilds, we nominate the 4th tank to take the plague and die with it during this phase, so you will most likely need to have a soulstone ready at all times and be prepared to apply it to the sacrificial scapegoat.Demonology: Metamorphosis on the pull, and it should be ready towards the end of the phase transition. Stand in melee range, saving immolation aura for the end of your time as Lollidan. Because you're constantly switching off PP to take out adds, use CoDoom over CoA until P3 (but you should have time for one full CoA in demon form before applying the stronger CoD - clip if you have to). Otherwise, good fucking luck. This fight's a bitch.
Pets: Your pet does not get the target-specific debuff for the phase transitions. It should always be on the volatile ooze, regardless of your debuff, to help soak the explosions.
