2 tank, 2 healers
DPS: Ideally you want no more than 2 melee. Any more than 2 and your ranged will have to have extremely strong AoE and slows/stuns/knock-backs/control to deal with Blood adds.
The big cheese of the Twilight Hammer. Cho'gall is a challenging but incredibly rewarding fight. There is one long phase that continues till Cho'gall hits 25% and then it turns into a burn phase with a small twist.
Why two healers? Just so you can push Cho'gall to phase 2 before the fourth cast of Festering Blood. You can accomplish this with 3 healers if your DPS is very, very high but your first kill will likely come with 2.
There are two major things you need to keep track of in this fight:
- Corruption: It's a debuff you gain through various abilities that starts at zero and goes up to 100. For the most part, you can avoid every way to gain corruption and go into phase two with zero corruption through tight play.
- Worship: Every so often, Cho'gall will target two people and they will begin to worship him. He will gain a stack of Worship for every 2 seconds that the worship goes on per convert, and each stack increases his damage output by 10%. This will destroy your tanks in short order. When worship is coming in, everyone needs to be ready to cast whatever AoE interrupt you can use to break it immediately. Howl of Terror, Dragon's Breath, Avenger's Shield, Frost Trap, anything like that, or even single target interrupts will work. This should be a very high priority.
Positioning Cho'gall is a big deal - where you place him will affect the way the fight goes and how you deal with adds. Most guilds seem to hold Cho'gall in the middle of the circle on the floor with everyone else in the raid grouping up right behind him.
We group up the exact same way but pull Cho'gall closer to the gate - about halfway between the center and the northern edge of the circle leading up the stairs. The reason behind this is so that you can draw the Corrupted Adherent up to the steps (which is where you want to kill them all) very quickly, and so that healers don't have to move at all to keep the Adherent tank in range. The problem with this is that your DPS has to be very much on the ball to be able to get all the blood adds down before they start hitting people, as the traveling distance is significantly reduced.
In addition to all this, Cho'gall requires a tank swap due to the Fury of Cho'gall debuff which increases damage taken by 20% for each stack, and he will also alternate two buffs on himself - Flame's Orders and Shadow's Orders.
So let's take it from the top. Once you pull and position him, make sure the entire raid is behind him in a tight clump and he is faced away from them with the two tanks in front of him. He will begin rotating his two Order's every few seconds. While he has Flame's Orders up, he will do a lot more damage to the current tank and splash a few fire puddles around the room that you might have to shuffle a bit for if the puddle winds up under the clump (this is the perfect time for Mirror of Broken Images!) When he has Shadow's Orders up, each of his swings will be accompanied with a shadow nova doing some unavoidable raid damage. This is the only damage that the raid should take during the entirety of phase 1 short of any light damage from interrupts for Worship. All other damage should be on the tanks.
His first cast of Fury of Cho'gall and his first summon of the Adherent tend to overlap a bit. Don't panic - continue tanking Cho'gall and don't move until he casts Fury. If the Adherent gets within range by then, the current Cho'gall tank can taunt it, the second tank should do nothing. Once Fury is cast, the second tank should taunt Cho'gall and the Cho'gall tank should begin dragging the Adherent towards the stairs.
As soon as the Adherent spawns, the raid should spread out as the Adherent will cast Shadow Crashes which is a source of both Corruption and damage - easily avoidable. All ranged should swap over as soon as it spawns and begin burning it down but it should not be killed until the tank has the add as far up the stairs as possible before Festering Blood is cast. Make sure you set up a rotation on the Adherent to interrupt the Depravity cast which will put a bit of Corruption on the entire raid.
The tank should begin running back to the clump as soon as the add dies (I tend to start running once it's sub 50k or so, since it'll explode a second later, but you might have to wait more or less a bit depending on your DPS - just feel it out) as it will leave a puddle behind that does damage and adds corruption (you move just before it dies because you don't want to wind up standing in this). The raid should also immediately collapse behind Cho'gall to ensure all adds stream towards the raid through any AoE and slows in a uniform manner (usually due to healer agro).
Very shortly thereafter Cho'gall should cast 2 things - his next Fury and also Festering Blood. The Adherent tank should wait for the Fury cast before taunting back or they will wind up with a second stack of Fury and the damage will get out of hand very quickly. (Note that Paladins can't bubble off the entire debuff!)
Festering Blood on the other hand is entirely on your ranged DPS. Put down every slows on the bottom of the stairs that you have available and begin to burn the adds as soon as they spawn from the puddle before swapping back to Cho'gall - if you are holding Cho'gall as close to the stairs as we do, having a knock-back or two will help a lot (Elemental Shaman or Balance druid or a Fire mage in a pinch).
During all this time, Cho'gall will continue to alternate his Orders and will periodically cast Worship, so that needs to be handled, especially when you're scattered to avoid the Adherent's Shadow Crash.
You will have a short while to DPS on Cho'gall before he summons another Adherent and casts another Fury. Rinse and repeat exactly as above making sure you avoid stacks of Fury, Crashes, interrupt Depravity, stack the Adherent blood pools as close together as you can manage on top of the stairs and interrupt worship. Every time he casts Festering Blood each puddle will produce 5 blood adds. So when the time the third Adherent dies, you will have to deal with 15 blood adds.
Once you get comfortable with this, and go through three Adherents, you should be ready to transition. When the fourth Adherent spawns, if you have Cho'gall low enough, all you will need to do is keep one ranged on it to interrupt his Depravity until it gets within melee range of the tanks and whichever tank is not on Cho'gall should just hold the add while interrupting his Depravity and all the DPS can burn Cho'gall down to 25% before he casts his fourth Festering Blood.
Once Cho'gall hits 25% the extra Adherent will despawn. This is probably a soft-enrage mechanic - make sure you have the DPS to get him down to 25% as a fourth Festering Blood will likely wipe you, either through the explosion if the fourth Adherent is still alive or with the 20 Blood adds that will spawn if it's dead.
As far as benchmarks go, we get our first Adherent with Cho'gall below 75% health, the second one with Cho'gall around 55% and the third around 40%. Remember that you will have one long period in the beginning of the fight to really focus on Cho'gall and once he summons an Adherent he will summon subsequent ones more quickly. Make sure your DPS (and tanks for that matter) Prepot (taking a potion just before Cho'gall is pulled so you can take another one later in the fight and use two that way), use all their big damage cooldowns right away and really burn him as best as you can.
On our best pulls, we've managed to get him as low at 65% before the first adherent spawns and pushed him into phase 2 just as the fourth Adherent spawns which makes life significantly easier for the healers. This will get easier and easier to pull off as your raid DPS gets higher and higher with gear and people become more comfortable with the rhythm of the fight.
Interrupt, scatter and swap to adherent, collapse and swap to adds, back to Cho'gall.
Just drill that over and over again and phase 1 will come under control.
Phase 2 is purely about raw bursts of DPS as Cho'gall will cast an unavoidable AoE that invariably stacks Corruption until everyone hits 100 and dies. This is why you want to go into phase 2 with as little corruption (ideally zero) on everyone. At a minimum, the most corruption you can manage to pull a kill off might be around 20 or so. Any more than that and you're in trouble.
We used a trick once on a really good pull when our mage wound up with nearly 40 corruption while the rest of the raid was ~10 as phase 2 loomed near. We asked him to jump into fire to die and then Battle Rez'd him to reset his stacks. I think we actually killed him on that pull, too. More advanced guilds use this mechanic to let classes with innate damage resistance (as 100% corruption will make you unhealable) get up to 100% corruption and do insane levels of damage to Cho'gall before dying and then using a battle res on them. We didn't feel this was necessary, but it's probably a tactic necessary for heroic mode with 4.1 gear levels.
As he gets close to 25% the tanks should move him as close to a wall as possible - we move him right next to the steps with his face into the wall. Every so often, he will summon four tentacles (which is why you want him against a wall - so the tentacles spawn a little more grouped up otherwise they'll be in a wide circle around him making AoE difficult). The Tentacles will target four random people and channel Debilitating Beam which reduces their Damage and Healing by 75% in addition to doing a bit of damage. No Bueno. These need to be treated like Worship - immediately interrupted and killed. They have a good amount of health (166k each) so make sure these got focused.
You can do this several ways - we have whichever tank is not on Cho'gall helping with interrupts and stuns while everyone else uses one of the DPS as a focus to single target and burn the tentacles rapidly before swapping back to Cho'gall but if your DPS is very high and the tentacles are clustered together, AoEing them down might also be an option for you. Keep them interrupted and stunned - those beams are vicious.
Keep your tank swaps going to maximize tank cooldowns and to keep Fury from stacking up. You should get a kill quickly as long as tentacles don't stay up for more than 10 seconds at the most. Now, as there is a ton of unavoidable corruption going out, you will start to gain corruption stacks, it is inevitable.
As people hit 25%, make sure healers are cleansing the debuff that will accelerate the rate of corruption. At 50% you will occasionally "feel sick" and 5 seconds later vomit, doing a fair amount of damage and adding corruption to anyone in front of you - make sure you turn away from the raid at this point! It is vital that this happens, you need to watch for this. It can be tempting to just try to burn through but you will kill people and wipe - even if Cho'gall is at 2% health, turn away. Trust me, we have lost very close attempts due to someone wanting to get that one last cast in. This will continue to happen periodically as corruption builds up - turn away every time and you will reduce the raid damage and corruption significantly. At 75% you will start doing some damage to the raid and at 100% you become unhealable but will have a very brief, glorious burst of damage as all spell cast times drop to zero and you do 100% extra damage. Just spam your nuke like crazy before biting it if you hit 100%.
That's really it - phase 1 may seem overwhelming at first, but drilling it a few times makes it simple. Tanking it is hectic, but fun once you get the hang of Fury swaps, and Adherent management. Corruption will be an issue at first, but you can manage it better the longer you pull, and interrupting Worship should always, always be top priority for everyone.
If you can get through Phase 1 with no one dead and low stacks of corruption - you can beat phase 2. You might wipe a few times in Phase 2 and it can be brutally frustrating - we had multiple sub 1% wipes and one 0% wipe in phase 2 before we got our first kill - 20k! Don't give up - if you're that close, you're basically there, just track Friendly Fire on Recount or Skada and make sure those people who're spewing on people are made aware of it, and keep phase 2 clean rather than panicking. Use DPS boosting potions, use Heroism, summon every pet you can to help, and burn - but keep your head and you'll soon be earning your tier shoulders.
This is a challenging fight, but incredibly fun and it makes a very satisfying conclusion to a fantastic raid. Bastion of Twilight, I think, is my favorite raid in this tier - the fights are challenging, there is a variety to them, all roles have something interesting to deal with in most fights and the gear isn't bad at all. Maybe a bit too much trash, but I'd rather have a lot of trash than no trash. Best of luck to you!