Cho'gall 10 & 25 Man

It's funny sometimes how you can bash your head against a boss for a couple of weeks and suddenly he just goes down, like that. We hadn't been doing that many tries on Cho'gall actually, but more than the average boss so far for sure. Therefore it was extra fun to manage to down him as fast as we did this time around. Had we really improved that much? And then, a couple of days later, we one shot him in my 25 man group. Half the raid were doing the fight for the first time and we haven't one shot a single boss so far, and this was a raid who wiped several times on Ascendant Council due to people not moving out of the raid with the Lightning Rod debuff, so that's just hilarious. What that tells me is that this fight is alot easier on 25 man than on 10 man. The tactics are the same, but there is one important difference (Worship) which I will discuss further down.

Cho'gall is a fight, just like Magmaw in a way, mostly about moving out of "shit on the ground" and handling the adds. Once you've got that nailed down, he's a goner. Unlike Magmaw however, Cho'gall doesn't just have two shit on the ground, and not just one set up of easily aoeable adds. Magmaw can be seen as Cho'gall light, but Cho'gall really has alot of things to think about. It still means however that he favors a raid group which can handle adds in a smooth way so yet again - a ranged heavy group is favored here. There are a range of tactics out there and I am not saying this one is the best - but it worked and we downed him.

Our raid comp was (when doing 10 man);

• Prot Warrior
• Prot Paladin
• Holy Priest (me)
• Resto Shaman
• Resto Druid
• Feral Cat Druid
• Balance Druid
• Affliction Warlock
• Fire Mage
• Unholy DK

Preparation
Like I've mentioned, Cho'gall is yet another fight that favors ranged dps. You want dpsers who can handle adds in a ranged manner because you want to avoid players getting too close to the small adds that spawn (more explanation further below). Cho'gall is a fight divided into two phases which differ quite much from eachother. The first phase is a typical "either be spread or stacked" kind of phase, like Maloriak. The second phase is a burn phase with some things to think about, again pretty much like Maloriak. Alot of the damage can be avoided, but you do need a certain amount of dps to be able to handle the adds fast enough.

Phase 1 - 100-25%
This is the more difficult phase in that there will be alot of things to think about. When Cho'gall reaches 25% he will go into phase 2.

Corrupted Blood - Most damage taken will increase your Corrupted Blood meter, kind of like the sound meter on Atramedes. The more Corrupted Blood you have the more damage you take from the aoe that Cho'gall does every once in a while. Corruption will also give you further debuffs the more you have, getting to a 100 Corruption will make you unhealable (among other things) but you should preferrably never even get to 50. Sufficient to say you should try to keep your corruption as low as possible at all times, and you do this by avoiding "shit on the ground". If you want to know exactly what every level of corruption does, check it out here. The Corruption seemed to stack alot slower in 25 man than in 10 man, so making mistakes was less forgiving in 10 man.

Shit on the ground - Cho'gall will empower himself with two different buffs during phase 1. The first one is a fire buff which will make him hit harder and spawn lava pools on the ground. Don't stand in them. The other is a shadow buff which will make his melee swings deal aoe damage and needs to be dealt with accordingly. This aoe damage is not very heavy in fact, and can be dealt with by a single focus aoe healer and one off aoe healer.
The big adds, also known as Corrupting Adherent, will spawn from the purple portals in the room. They will do a classical shadow crash with the benefit that you can see exactly where they will land, since there will be a purple swirl, just like on Valiona & Theralion, in that location. Move out of it.

Buffs and debuffs - There are a couple of debuffs and buffs (on the boss) that needs to be handled in a special way. Fury of Cho'gall will make the tank take alot of extra damage. To avoid having this on the tank currently tanking Cho'gall you will need to do a tank switch after this is cast. The new offtank will be the one handling the big adds. Accelerated Corruption is a debuff that looks just like the Corruption icon and is cast on players who have reached 25% corruption. This should be dispelled asap. Conversion, also known as Worship, will stun two/five (10/25 man) random players (not the main tank) and have them cast Worship. If they finish their cast Cho'galls damage done will increase for a short period. Worship is one of the trickiest things to get right in this fight, since it requires players to interrupt eachother. As far as we tried, any typical pvp interrupt will work towards doing this (Typhoon, Fear, Kick, Dragonbreath, Mind Freeze and so on). The interrupts used will stay on their targets for their full duration unless removed! This is really important to note because that means you want to use the interrupts that will interrupt the target the shortest amount of time. Fear for instance will stay on for 10 seconds unless dispelled. Hammer of Justice will have the target stunned for 6 seconds and so on. This was alot easier to handle in 25 man because wherever you were, someone else would be close to interrupt. This wasn't so in 10 man where it is alot easier to spread out and get out of easy range for your fellow raiders, so keep this in mind.

Adds - There will be one big add (Corrupting Adherent) spawning from the purple portals that need to be handled by the offtank. As soon as they are up, the raid should spread out to avoid shadow crashes. Remember to not spread out too much since you want to be close to someone in case you'll get the Worship debuff, which needs to be interrupted asap. They need to be killed before Cho'gall casts Fester Blood, otherwise they will wipe the raid. The Corrupting Adherents skills will also increase your corruption meter, and their skill Depravity should be interrupted. When Cho'gall casts Fester Blood, and if the big adds are dead, which they should be, 5 adds (Congealed Blood) per dead Adherent will spawn from the pool of black blood from the dead Adherent. These need to be nuked down asap, and you should avoid getting into melee range with them. Think oozes on Professor Putricide. Being hit by a Congealed Blood won't kill you, but it will increase your corruption meter fast. The Congealed Blood move very fast, so ber ready for that.

How to handle it all - this is how we did it;

1. Have tank A tank the boss in the middle of the room. You want to be placed stacked behind the boss, make sure you've arranged who is interrupting and who is interrupting the guy that is interrupting in case he gets into Worship. 
2. As soon as Cho'gall casts Fury of Cho'gall, have tank B taunt the boss, standing in the same place as tank A. 
3. When Corrupting Adherent spawns, tank A picks him up and tanks him towards the entrance. Not too close to the door since that will reset the fight as we noticed. All the way up the stairs does work though. Make sure to be in range of a healer, we had one healer follow that tank around. All dps will nuke the big add and interrupt the Depravity. 
4. As soon as the Corrupting Adherent is dead, everyone stack back up behind the boss. During all this you must remember to interrupt Worship. 
5. Just before Cho'gall casts Fester Blood, have all ranged ready to handle the Congealed Blood. There will be more Congealed Blood the more Corrupting Adherents you get, since 5 will spawn from each corpse. That means you'll soon be overwhelmed by Congealed Blood, and should aim at not getting more than 4 or so Corrupting Adherent during phase 1. 
6. Rinse and repeat until phase 2.

Phase 2 - 25-0%
This is a typical burn phase, but with a few things to think about.

Cho'gall will have a damage aura during this phase, which means there will be alot of aoe healing. This damage is in itself not overwhelming however, so don't waste your mana needlessly. Cho'gall will spawn four Darkened Creations, aka Tentacle Eyes, that need to be burned down asap (untankable). They cast a Debilitating Beam on a random raid member that reduces healing and damage done by 75%, deals a moderate amount of damage and stacks up Corruption (on your Corruption Meter).

This phase isn't too tricky actually, and if you get the first phase done in a smooth manner (ie don't get hit by stuff) this phase will be simple.

10 Man holy healing

25 Man disc healing

Priest specifics
Movement isn't that important in this fight, since you only have to either stack or spread (and move from the occasionaly fires/crashes), so I chose to use Inner Fire. In phase 1 most of the raid damage is avoidable, except when Cho'gall gains his shadow debuff. The aoe damage in phase 1 is fairly simple however, instead the tank healing is a little tougher. We had a designated healer for each tank and one who focused on a little bit of everything. The tanks will be spread out alot when the Corrupting Adherents come, so you might not have all healers in range for both tanks at that time. The tank can drop quickly and all healers should be ready for that. In the last phase there will be mostly aoe healing, but not so much that one has to spam aoe heals continously (not like last phase on Ascendant Council for example). Switching between stances for the tank heal and aoe heal is nifty on this fight, but you can get around with just being in Chakra: Serenity. For 10 Man I recommend holy for mana efficiency. Disc worked well in 25 man, and you can help out on adds in the last phase, but as you can see the healing throughput is alot lower and should be taken into consideration. I don't think recount can see the Bubble however. This fight isn't that tricky actually, because a failure isn't the end of the world. Instead all the failures add up into making the fight more and more difficult until it becomes unhealable. Except for getting aggro from boss/Corrupting Adherent, there are no one shot mechanics in this fight or attacks that deal a big portion of damage in one blow on anyone but the tanks.