The encounter relies on good tanking and high DPS. When properly executed, it is not very healing intensive.
4 tanks are recommended, and they must spec protection / feral instinct in order to generate as much threat as possible. 6 healers are also sufficient, especially in a raid where shadow priests are contributing towards healing the DPS classes. Unfortunately for melee classes, Void Reaver is yet another melee-unfriendly encounter due to his 360 degree melee range abilities. Bringing melee DPS classes increases the strain on healers and decreases raid DPS. However, since the enrage timer isn't particularly challenging, raids can easily bring 2 melee DPS class members. Shaman totems bring a lot of versatility to this encounter, bringing at least 2 shamans is recommended.
All standard buffs should be used: Improved Fortitude, Mark of the Wild, warlock imp and Improved Commanding Shout should be used to help those with a smaller HP pool, particularly melee classes that are susceptible to taking damage from the Pounding ability. Using Dampen Magic will slightly reduce the damage taken from Arcane Orb by ranged classes. Pairing shamans with the tanks is particularly beneficial for this encounter as Windfury Totem will help a great deal with aggro generation. Conversely, a Tranquil Air Totem for the highest threat generating classes (usually shadow priests) will also help a lot. When short on paladins, prioritize Salvation / Wisdom for the ranged DPS and Kings / Might for the melee classes.
Void Reaver has a 10 minute enrage timer, and about 4.5 Million HP.
Pounding is a point blank range area of effect attack that is channeled for 3 seconds, inflicting 1350-2250 arcane damage every second to targets in an 18 yard range. The cooldown on this ability is 12 seconds.
Arcane Orb is a random secondary target attack. Void Reaver will target a player and launch an Arcane Orb towards them. The orb moves at a reasonable pace, but players can run out of the area that will be affected before it hits. Upon landing, it does 4675-6325 arcane damage in a 20 yard radius, and also silences all targets in that area for 6 seconds. Targets in melee range or close proximity of Void Reaver cannot be targeted by Arcane Orb. An Orb is fired around every 3 seconds. They do not "track" players, but instead will land at the position where the targetted player was standing when the bolt was launched.
Knockback is a single target attack that is only performed on the target that currently has aggro (the MT). It punts the target back a small distance, but reduces threat by a large amount. The cooldown on knockback is about 30 seconds.
Void Reaver stands close to the western edge of his room, on the opposite side to the entrance. Engage him from the center of the room, with a hunter using Misdirection on the MT. Let Void Reaver come to the middle of the room while everyone else spreads out around him in a circle.
Positioning is very basic, with the tanks always keeping Void Reaver positioned in the middle of the raid, while the 5 groups spread out in a circle around him. Everyone should stand at the maximum range of their abilities, in order to maximize available space and travel time for the Arcane Orbs.
The encounter does not have different stages and is exactly the same from 100% to 0%. With Void Reaver tanked in the middle of the raid all players must be kept at full HP or as close to full as possible, in order for them to survive a 6300+ maximum damage Arcane Orb (for ranged classes) or a 6750+ maximum damage Pounding. Remember, however, that the objective is to minimize the damage done by these 2 attacks, both of which can be easily avoided by running away. Due to the aggro reduction by his Knockback ability, the main tank will lose aggro eventually, to one of the offtanks, who will in turn lose aggro when he is Knockback-ed. With 4 tanks, the first tank should have enough time to rebuild aggro before the 4th tank is punted and loses aggro. This tank rotation will continue until Void Reaver dies. Note that Void Reaver is not Taunt-able.
All warrior tanks should keep Commanding Shout and Demoralizing Shout refreshed for the duration of the fight. While off-tanking, try to build the maximum threat possible in a limited rage situation. Always stay in and take damage from Pounding as this will give you a healthy amount of rage that can be turned into threat.
Keep everyone's HP as close to full as possible. If a ranged class is hit by an Arcane Orb, or a melee class takes Pounding damage, bring their HP to full as soon as possible so that they can survive the next Orb/Pounding. Keep a close eye on the MT and the offtanks. While Void Reaver's melee damage is not too high, all tanks will take significant damage from Pounding, and must be healed within the 10 second window before the next Pounding. Also watch for aggro switching from one tank to another and readjust the healing effort to the new main tank as soon as that happens.
Avoid getting hit by Arcane Orb by moving as soon as possible. Not only will you lose most of your HP, but you will also be unable to heal for 6 seconds, putting the tanks at risk. Void Reaver will always target the players that will be selected for Arcane Orb a few seconds before the Orb is fired. Watch his target of target and move if you see your name.
Paladins should be ready to use Blessing of Protection if a ranged DPS class pulls aggro.
As a melee DPS class you must avoid taking Pounding damage, especially in a raid with several melee classes. You always have a 10 second damage window between Poundings. Pounding is spaced out every 12-15 seconds, giving you 2-5 seconds to run out of its 18 yard area of effect. When Pounding stops, run back in for 10 seconds of DPS. Rogues can also use Cloak of Shadows at the start of the Pounding to resist most if not all damage from the ability.
As a ranged DPS class, run away when targeted by Arcane Orb. Not only will you lose a significant amount of HP if hit, but you will also be silenced and unable to do damage for 6 seconds. Consider bandaging to regain your HP quicker, unless you get healed immediately. Void Reaver will always target the players that will be selected for Arcane Orb a few seconds before the orb is fired. Watch his target of target and move if you see your name.
Threat is an issue for high-threat generating classes, particularly shadow priests, so be careful: your threat will also be increased by healing your group members that get hit by Arcane Orbs. If you do pull aggro, remember Void Reaver cannot be Taunt-ed, so just run towards the middle of the room as soon as possible, and hope for a Blessing of Protection or for a tank to pull aggro off you. Aggro reduction abilities should be used whenever possible; hunters should Feign Death, warlocks should Soulshatter and mages should use Invisibility as soon as the cooldown is up.
As far as pets are concerned, they should not be used as they will take damage and immediately die when the first Pounding hits.