Thanks to Laqueesha
This is an encounter that, at least for first kills, will require absolute min-maxing of raid composition.
15-16 DPS (No more than 5 melee due to soaking requirements for Meteor Slash. At least one hunter.)
Raid Composition Commentary
Tanks: Can be either protection warriors or feral druids; a feral druid can help to boost damage with Faerie Fire and Mangle if one is not already included with the melee.
Healers: 2 Shaman, 2 priests, 2-3 paladins and 1 druid. Priests and 1-2 of the Paladins heal the main tanks; maintaining Inspiration on the main tank is necessary at all times. Shaman heal the damage the raid takes from Meteor Slash. The druid and 1 paladin should heal Burn targets.
DPS: Limit to 5 melee DPS. Warlocks can prove very useful in numbers here and stacking for absolute maximum DPS will be needed. Limit yourself to 1-2 Shadow priests; healers on the tank will need one due to Brutallus' damage output and spike capability.
Buffs and Consumables
All raid members must be fully buffed with flasks, elixirs, food, Haste Potions, Destruction Potions, and Ironshield Potions. Melee DPS classes should use old world Elixirs of Demonslaying. Drums of Battle are very useful and any raid members who can should be using them. All of these should be used on cooldown and a Heroism rotation should be developed and used. The raid must put out 27,777 DPS to beat the enrage timer.
10,000,000 Health, Demon, Taunt-able, 6 minute enrage timer. Brutallus himself has only a few abilities.
Chance to hit increased by 5%.
Enemy chance to dodge reduced by 20%.
This buff is currently active on all NPCs in Sunwell Plateau, including bosses, it seems intended to balance encounters against high avoidance tank gear. It also makes the rogue ability Evasion less effective. It does not require any particular raid strategy to counter, but tanks and rogues should be aware of it.
This is a 30 yard range fire based frontal cone attack. It has a 1 second cast time and a 12 second cooldown. It deals 20000 damage split between all targets within the cone, and applies a stacking debuff that increases fire damage by 75%. It lasts for 40 seconds. This cannot be resisted, dodged, parried or miss.
A fire based damage over time attack. At any point during the duration of the debuff, if the afflicted player moves within 2-3 yards of another player, they will spread a fresh debuff to the new player. Burn is randomly targeted. Damage starts at negligible amounts and increases every few ticks, culminating with a ~6000 tick at the end. The debuff lasts 60 seconds, can be resisted, and is removed by Cloak of Shadows, Iceblock, and Divine Shield.
This reduces the armor of Brutallus' primary target by 50% for 10 seconds and also deals 18850-21150 physical damage after mitigation. It will hit a well geared tank for approximately 5000. Note that this attack removes the Burn debuff.
Brutallus has a very fast attack speed and hits off hand and main hand. Without Stomp, his main hand will hit for 6-8000 and his off hand will hit for ~3000. During a Stomp they will increase to 8-11000 and 4-5000 respectively.
After 6 minutes Brutallus will gain a 500% increase to his damage and 150% increased attack speed. This will kill even Shield Wall-ed tanks.
The Raid will be split into 3 groups. The melee will be their own group; they will remain in the same position for the entire fight. Prior to the pull, or on early attempts, each melee should be assigned a position 2-3 yards apart so as not to spread the Burn debuff; Brutallus's tail can and will cover players up and obscure them from view, so moving is not advised. The other two groups will be group A and group B. The remainder of the raid should be split between each of the two tanks. Each of these groups should have between 9-12 players (counting the tank). As much effort as possible should be spent to keep the numbers even. Within each of these groups should be both healers and DPS. Healers should occupy the positions near the front while DPS stay near the back. All players in the raid should have an assigned position and should have no reason to move to anyone else's spot.
In addition to these are two initially unoccupied areas beside the melee group. This is the Burn areas where players in groups A and B will run to should they get the Burn debuff. Within the Burn areas players should remain spread by 2-3 yards so as not to respread their debuff. In this area the Burned players should continue to DPS and heal all out during their debuff. Healers will need to be placed in groups A and B so that they are in range of the Burn areas. Melee does not have to reposition as they should be spread enough to avoid spreading it and will not be soaking Meteor Slashes. This means they should be able to spend 100% of their time DPS-ing Brutallus.
This is a very unforgiving fight, the slightest mistake can be the difference between a wipe and a kill. All damage increasing debuffs should be used on Brutallus (Curse of Recklessness, though it will increase Brutallus' own damage, is necessary). Any debuff which will decrease the raid's damage will be tremendously helpful too.
The raid will position themselves in their spots and a hunter will use Misdirection to begin the fight. As soon as the tank has initial aggro, the raid should begin DPS. Any aggro pull, death, or disconnect will almost always result in a wipe.
Shortly after engaging, Brutallus will do his first Meteor Slash. Everyone in group A should be hit by it. If people are not, they should adjust to make sure they will take the next one. Following three Meteor Slashes, the tank in group B should Taunt. Tanks should offer a count of 3-2-1 over voice comms to allow healers to prepare heals on him. After three Meteor Slashes on group B, the debuff on group one should have worn off and at that point group A's tank should do as group B's tank did previously: count and then Taunt. That rotation will continue for the duration of the fight.
Throughout the fight, Brutallus will cast Burns. All healers and ranged DPS should move to the Burn spots shown in the diagram. It is imperative that those with Burn get out of the frontal cone immediately. Having the Meteor Slash debuff for the final few ticks of Burn will result in a death for almost anyone. The first few ticks are only for a few hundred, so the priority should be getting out of the Meteor Slash cone over getting to the safe spot. When a Burned player reaches the safe spot they should make it a point to make sure they are out of the cone: it is rather wide and completely lethal. Players must almost make sure not to spread their flame to players whose Burn has just worn off.
Along with Burn, Brutallus will cast another debuff, but only on his current target: Stomp. Healers should make sure to have the latest version of their boss mods that will give them a warning for incoming Stomps. Upon seeing the warning, all tank healers should immediately begin chain casting their best heals on the tank. A half second break in the heals can result in a tank death and a wipe. During a Stomp, tanks should use whatever trinkets they have and be prepared to use Last Stand or Shield Wall.
Rogue: Do maximum DPS. Use Cloak of Shadows on Burns to reduce the healing needed.
Shaman: For enhancement and elemental shaman, do the maximum DPS possible while buffing your group. For restoration shaman, heal the raid following Meteor Slashes, when there are no targets to heal for Meteor Slashes help on tank/Burn targets.
Paladin: Retribution paladins do maximum DPS. Holy paladins should either be healing the tank or Burn targets. Those on the Burn targets can begin by using Flash of Light and switching to Holy Light as the Burn increases. Healers on the main tank will have to chain cast higher rank Holy Light the entire fight. Use Divine Shield on Burns to maintain heals and reduce healing strain on Burn healers. Blessing of Light should be used on all healers to aid in Burn healing.
Priest: Shadow priests do maximum DPS. Holy priests should heal the main tank; they should be specced into Inspiration and be chain casting at all times to maintain the buff on the tank. This is key to dealing with the Stomp. Greater Heal should be used at almost all times with Prayers of Mending and Shields being tossed in on cooldown.
Hunters: Do maximum DPS, apply Scorpid Sting to reduce damage done.
Warlocks: Do maximum DPS, Curse Of Recklessness should be used in addition to Shadows Doom, and Curse of the Elements if there are enough mages in the raid to warrant it.
Mages: Do maximum DPS, Iceblock to save healers' mana on Burns.
Warriors: Tank or do as much DPS as possible. One warrior should have Improved Thunderclap and Improved Demoralizing Shout to reduce damage done. If a DPS warrior is brought he should preferably be arms specced to increase physical DPS.
Druid: Feral druids should tank or DPS and maintain Faerie Fire and Mangle on the boss at all times to increase raid DPS. Balance druids, if they can maintain the damage, should Insect Swarm and Faerie Fire and do DPS. A single restoration druid should be brought; if there is a lack of other healers two can be. Restoration druids should be responsible for keeping the Burn targets up through Heals over time and Regrowths near the end; should they have time they can place Lifeblooms on the main tank. If they can maintain it and there is no other druid, they should put Faeire Fire and Insect Swarm on the boss at least early on in the fight.
It can be helpful to have an alt priest and paladin logged out to provide an extra blessing and Improved Divine Spirit in between wipes as any little bit will help.
The mechanics are very simple but the execution is very difficult; it will take practice and sometimes luck to win.
Gear is of paramount importance; the requirements of this boss will exclude many players for no reason other than lack of gear. Make sure everyone in your raid has taken every possible opportunity to better their characters.
A first kill will likely be during an enrage. During the enrage, following tank deaths, paladins can Divine Shield and Taunt to try and push the last percent down.
This is a tough DPS fight. Stats for a typically close fight with Brutallus can be seen here. Stats of more Brutallus kills are available here (it will be most helpful to examine stats of guilds with similar gear levels to your own).