This end of tier/expansion boss has four very different phases in a big round room. Think of it as four simple bossfights back to back and take things calmly as they come one phase at a time. Also dying in early phases of this fight is not so bad thing for reasons explained below. Pictures stolen from Wowhead’s FatbossTV guide linked below and class table for adds phase from Epu’s post.

Phase 1 – 100% to 70%

First phase is all about void zones big and small. All of the voidzones will be cleared when phase 2 begins.

Cone of Death is a cone aimed on random non-tank that does big black voidzone from boss to the edge of the room. Because it’s any non-tank the plan is for everybody except active tank stack behind boss and that is the direction where the cone will be aimed at. Tank boss in the middle of the room and fill the piechart with blackness.

Soulblight Orb puts 8 second debuff on three random people who take damage and spawn voidzone below them when the debuff expires. Place these smaller voidzones on the path where next cone is going to spawn to maximize available space in the room.
Tortured Rage is on timer and does about medium shadow damage to whole raid. Not fatal alone, but combined with Soulblight Orb debuff will need extra attention from healers.

Sweeping Scythe is tank swap debuff. Switch after 3 stacks.

Golganneth’s Aid puts five second debuff on two random players, one will have watery ball hanging over his head and the other will have lightning ball. Once the debuff ends the balls will drop where the player stands and are stacking buffs that anybody can get for a short time. Water ball gives 2000 haste and versatility, lightning ball gives 2000 mastery and crit. One ball should be placed in melee group to minimize movement and another somewhere near ranged. Multiple balls will spawn during the phase and the effect stacks.

Phase 2 – 70% to 40%

Golganneth’s Wrath clears out all voidzones from the room but also damages players. There’s a small hole in the storm right in the middle of the room where raid needs to stay behind the boss and keep hitting it. After the storm clers boss and raid are immediately dragged to the edge of the room.

Edge of Obliteration summons very large spinning blades next to boss and marks big black streak on the ground. After few seconds blade goes through the black path and knocks back every player it hits. These are incredibly easy to avoid and there’s no excuse getting hit by one.

Phase 3 – Adds

Argus is imprisoned by Aman’Thul and summons seven Constellar Designates at the edges of the room, equal distance from each other. Raid is loosely stacked in the middle, and should be able to multidot all seven adds. These are normally immobile and untankable. Second potion here. Phase 4 will start once the adds are dead.

All seven adds have the same three abilities

• Cosmic Ray is beam that focuses on random player. Stand still and the rest of the group moves away from the beam’s path.
• Cosmic Beacon is short duration dot foollowed by explosion and dot on whole raid. Two of the adds will cast this at the same time. Raids needs to have 7 people assigned, one for each add to interrupt this and few reserves just in case. One missed cast will hurt, two missed casts is close to a wipe.
• Starblast is small interruptible damage on random people. This MUST NOT be interrupted on heroic or mythic mode, or it will make Cosmic Beacon uninterruptible and wipe the raid.

On timer two random adds will get Stellar Armory buff for a while and needs to be tanked and they do not use any of the three other abilities listed above. These two have threat they’ve got all phase long, and can murder melee dps if tanks are slow to pick them up. Melee should be moving bit away from their adds just before the Stellar Armory is cast.

• Blade of the Eternal increase melee damage by a lot. Tank who can take more physical hits better drag this to nearest other add for cleave fun.
• Sword of Cosmos increase melee damage by a little bit but it also gives long damage buff to any nearby adds. The other tank needs to drag this add to the middle of the room where it can’t buff the other six adds.

Discs of Norgannon debuffs the adds 15 seconds after the phase begins, each becoming vulnerable to one type of damage taking 200% extra. These are all fixed locations and raid should be split fairly evenly on these.

Physical : windwalker, warriors, hunters, rogues, enhancement, feral, guardian, retribution, havoc
Fire : destruction, brewmaster, fire, vengeance, havoc, elemental
Shadow : affliction, demonology, shadow & discipline priest, blood & unholy DK, havoc
Arcane : arcane mage, balance, guardian, havoc
Frost : frost mage, frost DK, havoc, elemental
Nature : mistweaver, balance, assasination rogue, havoc, elemental
Holy : protection pala, holy priest, holy pala, discipline, retribution pala, havoc

Phase 4 – 40% to loot

Everybody dies (kinda like Lich King at 10%), food buff and rune falls off and potion cooldowns reset. People can release and boss starts channeling End of All Things.

Gift of the Lifebinder

Eonar plants Gift of the Lifebinder tree in a fixed location in the room, and in the Spirit World players can see Hungering Soul adds wandering around. Touching these adds will knockback and slow you down but won’t damge… One perk of being dead. When you walk under the tree you will be ressed.

The tree has energy bar which drops every time somebody is ressed, and after the energy is gone it will get stacking dot every time somebody is ressed. Healers can keep it up while they can, but when the tree dies it’s dead and there will be no more free resses available. Save regular resses for tanks.

Right at the start of the phase everybody has to ress of course and get back to killing the boss. First thing is tanks getting some aggro on the boss and then interrupt End of All Things cast at the last second.

Boss ofcourse does new things in this phase.

Reorigination Modules are low health adds that spawn at the edges of the room. It’s player-sized blue ball which will grow void zone under it until its killed. When the ball dies it explodes for medium amount of damage, so try to stagger killing these to avoid killing whole raid. First time around there will be 3 balls, next time 4, then 5…

Mote of Titanic Power are smaller white balls that pop up in spirit realm in the areas where Reorigination Modules had their void zones. Collecting enough of these gives the raid Titanforged buff. Basically every time you die collect these that you see nearby but don’t bother running around finding all, instead return back to land of the living.

Deadly Scythe replaces the tanks’ Sweeping Scythe from first two phases. It does basically the same except hits for more and the stacks will never fall off. Tanks will stop swapping at any set number of stacks but instead they eat all the hits until they die, and then switch to the living one. While tanks are dead they should collect as many Motes of Titanic Power (the white balls) to boost up the raid and instead of ressing fast and come back only until last moment before the other tank drops dead.

Ember of Rage creates small blue swirly zones under random people. After short time crap falls on top of you and you’ll die. Simply move out.

Tortured Rage from phase 1 does a comeback. It’s still AOE damage pulse to whole raid. Healers take care of that.

Soulburst and Soulbomb from phase 2 does a comeback also. Follow the map and boss placement of phase 2. Except this time there’s no tank buff to save Soulbomb victims. If you don’t have personal cooldowns to survive just release, collect Motes and ress back up.