2 Tanks, 3 Healers
This is a really, really fun fight. I enjoy this a lot no matter how many times we kill him. Dynamic, fluid, and challenging, but not too tough. But. He hasn't dropped my mace yet. So I'm upset at him. -_-
One tank on the boss, another tank on the adds, 3 healers and any configuration of DPS but the more interrupts and ranged you have, the better. I usually tank Maloriak on this encounter and I take all of his AoE interrupts - it's very easy to do and the Maloriak tank shouldn't waste DPS time with it.
The tricky interrupt is the Release Experiments one. Assign a dedicated interrupter for this. You want the first set of adds in phase 1 (say, Blue) then interrupt the rest, and you want the first two set of adds in the next phase (Red), then interrupt the rest. In Green phase, you should still be interrupting the AoE's but have at least one other person targetting Maloriak so that any more summons get interrupted. You do not want any summons in Green phase. We usually have a DPS do this as we can afford to loose one person on the adds and still get them down very easily.
Red phase - gather up on Maloriak tank, move out far to the side if you have the Engulfing Flames debuff. Ocassionaly the Maloriak tank will get it and obviously they can't move so make sure you hit a heavy cooldown.
Blue phase - spread out, and for Pete's sake, wait for the person getting hit with tomb to be topped off before breaking the tomb. Don't you remember Sindi? Jeez.
Green phase - we actually begin moving to AoE the adds a touch before green to take full advantage of the damage buff from green phase. We hold Maloriak off to one side while everyone kills the adds then swap over to Maloriak.
If you have 12 or 6 adds in the first phase, it's still doable, have the add tank hit a really big CD while gathering the adds just before the Green phase and have them kiting them the rest of the time with some help from your mages and hunters and shaman with snares and slows across the back of the room. Worst case, you can have a plate DPS pick up 3 and hold them to one side while the tank holds 9.
Our group usually has Maloriak at about 30% around the second Green phase and we make sure to clean up all adds before burning him to 25%. If you transition him early with the minions alive and your add tank has to hold them and the Prime Subjects at the same time, you're probably going to wipe. Just relax and wait for adds to die, even if it means Maloriak goes into a red or blue phase - you'll push him into phase 3 soon enough and the enrage timer is super generous.
Phase 3 is an easy burn phase. Keep Maloriak by his cauldron faced into the wall, everyone should be close to Maloriak except the add tank who holds the Prime Subjects towards the front of the room near the steps so they only fixate on him.
The Maloriak tank should dodge the Magma Jets - go into DBM and turn on the announce - you are not meant to be healed through that. Strafe, and you'll be able to keep him in one corner of the room easily, faced away from the raid, as the fire on the ground dies out fairly quickly. Don't be afraid of using your CDs to stay alive - if you die, the other tank can hold the adds and boss for a very short while but it's not easy by far. As long as the raid dodges the white snow balls, there is very little raid damage other than some mild, latent AoE - Hero and burn him before your healers run OOM from keeping the add-tank up while he's being fixated by the Prime Subjects.
2 Tanks, 3 Healers (can be done with 1 tank)
I like this fight in theory and I hate it in execution. It's entirely on the shoulders of your healers and you can't do much to help. Sure, you can WoG yourself to stay above 10% but that's about it if you don't want to spend a ton of time regaining mana. Still, it's the best contribution we can make to the fight.
Make sure you're looking at your heal comp and if you've got more than one restoration druid, it can be a bit messy. You might want paladins or holy priest to spec out of DPS to heal, and have your extra resto DPS instead. Just mechanically, druids are good for tank heals but lousy for raid heals. They can't get people up to 10k quick enough with HoTs and Nourish spam will make them go OOM. That said, Tranquility is awesome for Feud and even non healers should hit it on a rotation.
Also, make sure that your DKs, Warriors and Warlocks take their self-harm for damage buff abilities off the bars. They will kill themselves. Many times over. Remind them before you pull and make them take those abilities off their bars. Muscle memory will kill them. Trust me.
Start with specific assignments and split your raid into three groups - 1 healer with 2 tanks, 1 healer with 3 DPS and 1 healer with 2. Make sure the assignments and positioning are explicit and only ask for cross-heals if a healers group is topped off - each healer is responsible for themselves and their group first and the other groups later. It's like those oxygen masks in airplanes - help yourself first before assisting the healer next to you! Trust the other healers to manage their group.
Massacres will require quick healing of the whole raid and everyone should do their part to use any self heals right after the Massacre.
Assign one melee tank and one Double Strike tank. The melee tank will have him 95% of the time and only needs 10k health at any given point (except for Feud, of course). The Double Strike tank will take all the Double Strikes and is the only person who needs to be topped off (or close to it) at all times. The DS tank should taunt as soon as Chimaeron gets the Double Strike buff, eat that hit, then the melee tank taunts back. Make sure the taunts are clean, setting up raid frames to show your targets buffs helps immensely with this. This is not a DPS race so neither tank out threat the current tank. Sit and swing, you're a leaf on the wind, the damage is manageable, trust your healers.
The melee tank role is the one you can swap an actual tank out for a plate DPS with Fury or Blood Presence on if you really want a lot more DPS in phase 3 as the incoming damage really isn't mitigated anyway and 10k health is 10k health, whether on a tank or a DPS but your mileage may vary. We use two tanks just because it's simpler that way and because Paladin tanks bring a ton of raid utility as you'll see below.
When he enters a Feud phase, group up on the tanks and make sure you healers follow their big AoE heal rotation - you might have a Holy Priest take the first one, a Shaman take the second, a Discipline Priest take the third, etc. and if you have DPS with any AoE heals (Druids, Paladins, Shaman) or damage reduction abilities (Antimagic Zone, Earthclaw Totem) make sure they get used as well and get the whole raid as close to topped off as possible. Once the three caustic slimes go out, everyone goes back to their original starting spots. This cycle repeats till he's ready to transition.
When he hits 27% or so, you need to take a look at your timers and decide what to do - if another massacre is imminent wait for it to hit, heal up and then push for transition, otherwise go ahead and push through, but you need to make that call early and commit otherwise you might get hit with a massacre just as he pushes over and you're done. It might be easiest to get him low, wait for a Massacre then push as the raid is getting healed up to full, but it will depend on your group - discuss with healers!
Phase 3 is all about the fastest burn you can put out. Remind healers not to heal but to wand or moon fire spam or something. If you can catch him in a Feud just as he transitions, I guess you might be able to get him super low before he casts Mortality but I personally wouldn't risk it.
I know I said we can't do much, and honestly, all of this off-healing and mitigation helps doesn't amount to much, it's nice to have, but at the end of the day, your healers have to do horrific amounts of triage to keep the raid up above 10k or topped off depending on the phase, and it's tough on them. Give them a hug after this - they'll be whimpering and shaking.
DPS on the other hand can really tunnel-vision and hit their rotation perfectly and only move to group up every time you have a system failure. Gather with the tanks so melee can keep, uh, meleeing. This is as close to a Patchwerk fight as we get these days, I suppose.