I'm working on getting some new guides up (though the information on the Beta Raid Previews pages are still relevant) and thought I'd kick it off with Chimaeron in Blackwing Descent.
Video: One of our Chimaeron 25 man Heroic kills. Details on the Heroic mode are towards the end of this post after the normal mode description.
Chimaeron is one of the three bosses inside Blackwing Descent beyond the entry gate - after defeating the Omnitron Defense System and Magmaw, the portcullis will open and allow you to face Chimaeron, Maloriak, and Atramedes before facing the final boss, Nefarian.
Chimaeron is a mix of simplicity and difficulty - the concept and strategy to the fight is straightforward, but the actual execution can be quite challenging. While DPS have a fairly straightforward burn throughout this fight, tanking and healing have some unique challenges which I'll cover after the ability and strategy breakdown.
Let's start by taking a look at Chimaeron's abilities. (source)
Finkle's Mixture - Damage taken while above 10,000 health cannot reduce your health below 1.
Caustic Slime - Deals 280,000 Nature damage and reduces chance to hit for all enemies in an area. Damage is split between all enemies with 6 yards of impact.
Massacre - Inflicts maximum damage to all enemy players.
Double Attack - Chimaeron will strike twice on his next attack.
Feud - Chimaeron's heads are fighting each other and are unable to perform melee attacks.
Break - Increases Physical damage taken by 25% and reduces healing by 15% for 1 min on the target, stacks.
Mortality - Chimaeron goes into a rage, becoming immune to Taunts, increasing his damage taken by 20%, and reducing healing effects for all enemy players by 99%.
Double Attack - Chimaeron will strike twice on his next attack.
The key mechanic in this fight is Finkle's Mixture. This is a raid-wide debuff that is enabled when you activate the Bile-o-Tron by speaking to Finkle Einhorn, the gnome in the cage at the back of the room. Once you speak to Finkle, the Bile-o-Tron will switch on and begin moving around the room. Chimaeron will begin to wake up, however, you can speed things up by engaging him directly.
It is extremely important to spread out at least 6 yards apart for all of phase 1. This should ideally include melee, who can spread out around the boss' hitbox. This is to prevent Caustic Slime hitting more than one target at a time, as the splash damage can kill even if the initial hit doesn't. While the Bile-o-Tron is active, Finkle's Mixture will prevent everyone in the raid from dropping below 1 health if they are at or above 10,000 health. This allows the raid to survive the Caustic Slimes and Massacre.
The Bile-o-Tron will periodically be knocked offline during phase 1. When the Bile-o-Tron is knocked offline, the raid is no longer protected by Finkle's Mixture, so the raid needs to stack up and be healed fully. There will still be Caustic Slimes and without the Bile-o-Tron raiders can die from it, so they must be healed up. It is also extremely important the raid is tightly stacked - this will mitigate the damage from Caustic Slime on the raid.
As soon as the Bile-o-Tron is back online, the raid needs to immediately spread back out to again avoid splash damage from Caustic Slimes.
Phase 2 begins when Chimaeron hits 20% health. At this point, it is simply a DPS burn. Chimaeron becomes immune to taunts but takes additional damage. Healing is reduced by 99%, so basically no one will be getting healed during this part of the fight and people will die. He moves slowly, so he can be kited, but he needs to be burned before raid members begin dying. The Bile-o-Tron will still be active, so you'll have the Finkle's Mixture buff, but you won't be able to heal anyone back up above 10,000 health once they fall below it.
You'll need two tanks for this fight on normal mode to deal with two of Chimaeron's abilities: Break and Double Attack. These two abilities affect Chimaeron's targets and specific tank taunts will effectively deal with this.
You can use the Finkle's Mixture to your advantage here. The Main Tank can tank Chimaeron and take the Break debuff. So long as the MT is kept above 10,000 health, if the Bile-o-Tron is online the MT will not die. The MT only needs to be kept above 10,000 health. Even with multiple stacks of the debuff, if he's above 10,000 health, he won't die while the Bile-o-Tron is active.
The key here is the Off-Tank. The OT will be taunting Chimaeron in order to take the Double Attack only. The OT must be kept topped off at full health. Because the Double Attack is two strikes, even if the first hit doesn't kill the OT, the second one can easily kill if the OT falls below 10,000 health.
In normal mode, Chimaeron will Feud while the Bile-o-Tron is offline and will not deal any melee attacks, so your tanks should be healed up along with the rest of the raid but won't require special attention until after Feud is over when the Bile-o-Tron is back online.
Chimaeron deals massive strikes to the tanks, so it is important both tanks and healers be ready for these hits and rotate cooldowns as needed. Good avoidance and mitigation for tanks is great on this fight - dodging one of Chimaeron's big hits is fairly obvious.
I've touched on one aspect of healing this fight above in the tanking section. This fight is fairly specific in terms of healing strategy and hinges on the use of Finkle's Mixture.
While Finkle's Mixture is active when the Bile-o-Tron is online, the raid will not drop below 1 health - as long as they are above 10,000 health. The entire raid needs to be kept at 10,000 health minimum and, ideally, maximum. Do NOT waste mana trying to heal everyone up to full in these phases - you will burn yourself OoM.
When players are below 10,000 health, they will gain a debuff called 'Low Health'. For those of you using addons such as Vuhdo and Grid, you can enter this debuff into your customizable debuffs and it will show up on players below 10,000 health. (You can see this debuff indicator on my Vuhdo frames in my video at the beginning of this post).
At lower gear levels, our cheap heals (Nourish for druids, Heal for priests, etc) will likely not heal targets up over 10,000 hp unless they crit (most will hit for around 8k), so you will likely have to try different heals to get targets healed quickly enough. You'll have about 5 seconds between the different abilities (Slimes and Massacre). You may want to try heals like Healing Touch, Rejuvs, etc.
It is extremely helpful to assign healers to groups to prioritise targets hit by Caustic Slime and Massacre and to avoid missing some raid members when you have overlaps on other targets. Having healers prioritise certain groups or targets first and assisting other targets/groups when they can is useful. Also be aware of healers who can heal themselves while healing others, such as Priest's Binding Heal. You may also find it helpful to run extra healers, especially for early attempts and kills, as adapting to the healing strategy will likely be the most challenging part of this fight for many raids.
When the Bile-o-Tron is knocked offline, the raid is no longer protected by Finkle's Mixture. It is imperative the entire raid stacks up tightly to mitigate the Caustic Slime damage. During this phase, the entire raid needs to be healed to full - AE heals like Efflorescence, Wild Growth, and other class abilities like Holy Word: Sanctuary, Healing Rain, etc are extremely useful in this phase. If you have several druids, you may find rotating Tranquility in each collapse is helpful. DPS classes can also throw out a quick AE heal if they have it to help (such as ele and enhance shamans throwing out a Healing Rain). Once you top the raid up fully the first time after Massacre hits, you can likely heal the raid up to about 85% and on downwards from there for the remaining hits to conserve a bit of mana, as there will be a only a few Caustic Slimes hitting the raid before the next Massacre and the Bile-o-Tron coming back online.
When the Bile-o-Tron is back online, the raid should spread back out and again be kept only at 10,000 health.
As mentioned in the Tanking section, the Main Tank tanking Chimaeron can be kept just above 10,000 health. The Off-tank taking the Double Attack hits must be kept at full health, though, in order to prevent him from dying to the Double Attack.
Once you hit Phase 2, all healing is reduced by 99%, so any heals are pretty futile at this stage. You'd likely be most useful by helping with the DPS burn. For Druids, using Tree Form as a DPS cooldown in Phase 2 can be helpful in the DPS burn.
And that is it for the fight! It's fairly simple in concept - spread out, collapse, repeat, and pewpew, really - but it will likely be a gear-check for many and will test tanks and healers as well as DPS, who need to burn him at a decent pace (especially if sacrificing some DPS for additional healers).
There are two significant changes from normal mode to Heroic mode.
The first extremely important difference is Chimaeron no longer does Feud - Nefarian appears and interrupts it, allowing Chimaeron to attack.
This means Chimaeron will melee the tanks while the Bile-o-Tron is offline.
Your tank rotation for Break and Double Attack become of much greater importance on hard mode.
There are several ways to manage this change, all involving important tank rotations in addition to solid healing and damage mitigation cooldowns.
It is easiest, especially in 25 mans, to run three tanks for this fight on Heroic. One tank will continue to be the Double Attack tank only - he will only taunt Chimaeron to take the Double Attack strikes. This tank needs to be topped off at full health throughout the fight and should never get the Break debuff.
Your other two tanks will be your Break tanks. It is crucial to survival that the person tanking Chimaeron while the Bile-o-Tron is offline not have any stacks of Break when they taunt - they will die very quickly if they are taking melee hits from Chimaeron while the Bile-o-Tron is offline. A simple way to handle this, then, is to have one of your Break tanks begin the fight tanking Chimaeron. They will continue to do so up until the first Feud, which generally leads to about 4 stacks of Break. The second Break tank then taunts Chimaeron at the start of Feud. The second tank can continue to hold Chimaeron when the Bile-o-Tron comes back online until the next Feud, by which time the first tank's stack of Break will have cleared, allowing the first tank to taunt Chimaeron for the following Feud.
In summary, you have your Double Attack Tank (DA Tank), offtank 1, and offtank 2.
OT 1 begins the fight, DA Tank taunts for all Double Attack hits.
Feud - OT 2 taunts, DA Tank taunting as needed for Double Attack still.
2nd Feud - OT 1 taunts, DA Tank again taking Double Attack strikes.
3rd Feud - OT 2 taunts, DA Tank taking Double Attack.
and so forth. This sort of rotation should ensure your tanks are clear of the Break debuff when they are tanking Chimaeron while the Bile-o-Tron is offline.
The tanks will need to be topped off during Feud in addition to the normal raid healing, and the tanks must be quickly topped off after the Massacre before Feud in preparation for Chimaeron's first strike. A cooldown such as Guardian Spirit, Pain Suppression, or Hand of Sacrifice is also crucial when the OT taunts to help mitigate the incoming damage. You can see in the Heroic video at the top of this post (where I am tank-healing) how quickly we're working to get the tanks topped off for those phases.
Note: I have not tried the following strategy suggestion for 10 mans (as I'm currently doing primarily 25 man raids) - if any have used this strategy or a similar one, please do let me know and I can update this suggestion. :)
10 mans may feel a bit pressed to get 3 tanks into their raid, and it may be feasible to work out a tanking rotation that utilises a DPS class (Plate would likely be preferable) as their third tank. The DPS would only feasibly be able to tank while the Bile-o-Tron is online (as they will not have the mitigation or crit immunity to survive melee hits while it is offline). It may be possible, then, to have the DPS be the dedicated Break tank and always tank Chimaeron while the Bile-o-Tron is online. The Off Tank (an actual tank) would then always (and only) tank Chimaeron during Feud while the Bile-o-Tron is offline. The Double Attack tank remains the same and only taunts for Double Attack. This should theoretically provide time for the Off Tank to clear the Break stacks obtained during Feud stages. The Feud timer is slightly different and more random in Heroic mode, though, which may pose issues. Playing with rotations to find what works best for your raid is recommended!
There will still be Caustic Slime damage incoming to the raid during Feud while the Bile-o-Tron is offline, so raid cooldowns such as Power Word: Barrier and AoE heals like Efflorescence and Healing Rain are extremely helpful.
The other main difference in the Heroic mode is in Phase 2. Nefarian again appears to spice things up a bit.
Throughout Phase 2 (Chimaeron sub-20% health), Nefarian will cast Mocking Shadows which inflicts 1000 Shadow damage to all raid members every second.
This ability is, of course, combined with the normal Phase 2 debuff Mortality, which reduces all healing by 99%. It is essential the entire raid is topped off as you push into Phase 2. This gives crucial extra time to burn Chimaeron before too many raid members begin to die. Timing the push into Phase 2 is also important, and it is generally best to do so after healing the raid up to full immediately after a Massacre. After Massacre hits you will have about 5 seconds to top up the raid and push him into Phase 2 before Caustic Slime hits the raid and reduces raid member's health. Healthstones are best saved for this part just before Phase 2, and personal damage mitigation cooldowns (Anti-Magic Shell, Barkskin, etc) are best used in Phase 2 to reduce damage taken from Mocking Shadows. Disc Priests can be very helpful in Phase 2 as well as their Power Word: Shields will absorb much of the damage, helping mitigate raiders' damage taken rather than futilely attempting to heal through Mortality.
Good luck and have fun!