At the center of Ny'alotha stands a dread mountain of flesh, teeming with eyes and tendrils of unfettered corruption. Madness itself seeps from the writhing mass, eroding the sanity of all who approach it. This is the heart of the Black Empire, N'Zoth's seat of power, the body of a god.
This is a three phase encounter where you will be fighting the Fury of N'Zoth however in each Phase of the encounter you will be dealing primarily with the other elements of the encounter.
You will have a 
Sanity bar when starting this encounter which will be drained from a variety of mechanics during the encounter, however you are able to re-fill the sanity bar with the support of Wrathion who will be standing at the start of the encounter area for each Phase.
Anchor of Sanity - Wrathion will have a field around him which will restore Sanity to any players stood within it. You will also receive a movement speed buff whilst in this zone called 
Grace of the Black Prince which lasts for 10 seconds. The rooms for each phase are quite large so it is advised where possible to have a Warlock gateway set up between Wrathion and the centre of the room.
Ashjra'kamas, Shroud of Resolve - You will have an extra action button to use your cloak. This is on a 2 minute cooldown and will transport you to Wrathion. It will also heal you for 100%.
If your Sanity ever reaches 0 you will gain the 
Gift of N'Zoth buff which will provide you with a 100% increase to your damage and healing done for 20 seconds. However, when this buff expires you will become a 
Servant of N'Zoth, have 100% increased health, and repeatedly cast 
Mental Decay on players in the raid which will reduce their Sanity.
Mandible Slam - This is the tank swap for this encounter, each hit will deal large amounts of Physical damage and applies a stack of 
Black Scar which deals large amounts of Shadow damage, whilst increasing the amount of damage you will take by Black Scar by 100% per stack.
Madness Bomb - Several players will be targeted with this mechanic and have a visual ring around them. After 12 seconds it will expire dealing heavy Shadow damage and fear all players within 10 yards for 2 seconds. If you were not the target of this, you will lose 30 Sanity.
Adaptive Membrane - One of the mobs in the encounter will receive this shield for 12 seconds which will place an absorb on the mob and prevent them from being Crowed Controlled or slowed below 100% movement speed. If the shield is broken before the duration of it expires the damage taken will be dealt to the target, and a 
Fragment of Sanity will spawn.
Fragment of Sanity - When you touch this orb you will have 10 Sanity restored.
[Heroic] The target of the Adaptive Membrane will also be immune to interrupts.
Mental Decay - This will target a random players in the raid and drain 15 Sanity and place a 12 second light Shadow damage DoT.
There are two tentacles in this phase which the raid must deal with as the highest priority. When these are killed Fury of N'Zoth will take damage.
Growth-Covered Tentacle
Growth-Covered Tentacle - This will slam down from one side of the room to the other, you will see a large shadow appear on the floor on the location that it will slam towards. If you are hit by the Tentacle you will take a lethal amount of Nature damage.
The raid will need to be spread on either side of the tentacle to kill the 
Horrific Hemorrhages. If any Horrific Hemorrhages remain after 1 minute, they will deal very large amounts of Shadow damage to the raid for each one alive.
The Horrific Hemorrhages will also spawn puddles in the room which spawn Nightmare Antigen adds.
Nightmare Antibody - This debuff is applied by the melee swings from the Nightmare Angigens and deals a moderate amount of Shadow damage, reduces your haste by 3%, and reduces your movement speed by 3% per stack.
Adaptive Antigen - The Nightmare Antigens will periodically gain this buff which increases their damage done by 10% per stack and prevents them from being slowed below 10%.
Interconnectedness - When all Horrific Hemorrhages have been killed the boss will lose 1.25% Health for each Horrific Hemorrhage.
Gaze of Madness
Breed Madness - This add will repeat this ability endlessly. This is a channel that will go onto multiple targets and deal increasing amounts of Shadow damage over 9 seconds. This can be interrupted, however when the cast ends (either by completing or being interrupted) the add will cast both 
Maddening Eruption and 
Deepening Madness.
Maddening Eruption - This drains 5 Sanity from all players and deals a moderate amount of Shadow damage.
Deepening Madness - This increases the damage from Maddening Eruption and Breed Madness by 5% per stack.
Interconnectedness - When the Gaze of Madness has been killed the boss will lose 3% Health.
Important: Ensure you are on as much Sanity as possible when finishing this phase, as in Phase 3 you will no longer have Wrathion's Aid.
You will not be able to attack the Fury of N'Zoth in this phase until you have destroyed all of the Synthesis Growths on the sides of the room. Whilst the Synthesis Growths are alive the Fury of N'Zoth will heal any missing health.
Synthesis Growths
These are placed on both sides of the room on the ramps and at the top of the room, they will all be casting 
Synthesis which grants the boss immunity to damage, immunity to healing reduction effects, and heals him.
Mycelial Cysts
Mycelial Growths - Webbing will emit from the Cysts which will reduce your movement speed by 75% and deal moderate amounts of Nature damage if you are stood in it. The size of the webbing reduces as the health of the Cyst decreases.
Regenerative Mass - The Mycelial Cysts will regenerate 1% health every 0.5 seconds.
Fury of N'Zoth
Mycelial Infusion - If the boss is stood within the Mycelial Growth he will gain 100% increased damage.
Eternal Darkness - This will deal a moderate amount of Shadow damage and drain 5 Sanity from all players in the raid. It will also cover your screen in a completely horrible graphic of the Eye of N'Zoth for half a second.
Occipital Blast - The boss will face in the direction of a player and cast this ability. Any players caught in it will take heavy amounts of Shadow damage and lose 40 Sanity.
During this phase you will no longer have the help of Wrathion.
Madness Bomb is now replaced with 
Insanity Bomb.
Eternal Darkness is now replaced with Infinite Darkness.
Insanity Bomb - This functions in the same way that Madness Bomb does, but applies to everybody in the raid. When the Insanity Bomb expires it will also spawn 1 Nightmare Antigen.
Infinite Darkness - This functions in the same way that Eternal Darkness does, but drains 10 Sanity (up from 5). It will also spawn an 
Infinite Void which will deal stacking amounts of Shadow damage to players who are stood within it.
Thrashing Tentacle - Three tentacles will spawn around the edge of the room and slam towards the centre of the room, you will see a large shadow appear on the floor on the location that it will slam towards. If you are caught within these you will take lethal amounts of Nature damage.
Please note: No testing has been conducted on this boss for Mythic.
All Phases
Adaptive Membrane - This can now be placed on players, which will make it more problematic to remove the absorb shield. When the absorb has been removed both a Fragment of Sanity and a 
Shard of Sanity will spawn.
Fragment of Sanity - This now restores 5 Sanity to a player (down from 10).
Shard of Sanity - This restores 10 Sanity to all players within 20 yards.
Phase 2
You will no longer have the help of Wrathion for both Phase 2 and Phase 3.
Reactive Mass - This buff makes the Mycelial Cysts untargetable for 18 seconds, once the buff expires it will cast 
Regenerative Expulsion.
Regenerative Expulsion - This will heal the Cyst by 100% and deal heavy Shadow damage to all players within 15 yards.
When you kill a Synthesis Growth, 2 Nightmare Antigen adds will spawn.
When you kill all Synthesis Growths Phase 3 will begin.
Phase 3
Mycelial Cysts are present in this area of the encounter
All Phases - Swap at 2 stacks of Black Scar (Please note: on Normal/Heroic you will need to swap at 3 stacks in Phase 1)
Phase 1 - Position the boss near the tentacles when they spawn
Phase 1 - When the Growth-Covered Tentacle slams down be prepared to pick up adds from the red puddles on the ground
Phase 2 - Keep the boss out of the Mycelial Growths to ensure he does not get the Mycelial Infusion buff
Phase 3 - Be prepared to pick up adds after every Insanity Bomb
Phase 3 - Keep the boss out of the shadows of the Thrashing Tentacles
You can dodge Mandible Slam, however you will still gain a stack of Black Scar
Black Ox Statue can be useful to group the adds together in Phase 1 and 3
Provoke is useful on this encounter to move the boss towards adds faster for more optimal cleave
Tiger's Lust will allow you move at full speed when you have Nightmare Antibody stacks
Sigil of Chains can be useful to group the adds together in Phase 1 and 3
Avoid casting 
Avenger's Shield on the Gaze of Madness, as each interrupt drains Sanity from the raid.
Mandible Slam is blockable
The Black Scar debuff can be negated if 
Blessing of Spellwarding or 
Divine Shield is active during Mandible Slam
Divine Shield will remove all stacks of Black Scar and Nightmare Antibody
Blessing of Freedom will allow you move at full speed when you have Nightmare Antibody stacks
Mandible Slam is blockable
Shockwave can be useful to stun the adds that spawn in Phase 1 and 3 once they are grouped together to prevent them from attacking the raid
The Black Scar debuff can be deflected if 
Spell Reflection is active during Mandible Slam
The Nightmare Antibody debuff can be deflected with Spell Reflection
You can dodge Mandible Slam, however you will still gain a stack of Black Scar
Stampeding Roar is very helpful on this encounter as the rooms are large and there is a lot of movement between Phases
Ursol's Vortex can be useful to group the adds together in Phase 1 and 3
Gorefiend's Grasp can be useful to group the adds together in Phase 1 and 3
The Black Scar debuff can be negated if 
Anti-Magic Shell is active during Mandible Slam