This is a 3 Phase encounter and each phase is pretty unique, so I am going to breakdown each phase on its own.
Phase 1: In this phase you’ll have access to your on-use cloak as an additional boss button in the fight that will restore all of your Sanity and instantly heal you to full. This phase is similar to its heroic version, however the tentacles that slam the ground spawn in set locations on Mythic, making this phase even more scripted than its heroic version. The first set of tentacles that spawn will have 4 tentacles – 2 of them slam down in the front and 2 of them slam down in the back, separated by a small gap in the center. You still need to kill all of the Horrific Hemorrhages that spawn on them so that they disappear. The second set of tentacles will spawn in a V formation, cutting off your ability to get to the back of the room near Wrathion. To counter this, you can either leave before the tentacles slam down, or use your cloak to teleport to the back of the room. There will also be 2 Gaze of Madness adds each time they spawn, and each needs to be killed quickly to limit the sanity loss and damage that they deal. Generally you want to interrupt each of them at least once as soon as the channel of Breed Madness has begun (not the cast of the spell) to limit sanity drain and damage done. Like heroic, Madness Bomb will periodically fear 3 players, so if you or someone you’re close to is affected you can use Tremor Totem to break the fear.
Phase 2: At the start of Phase 2 every players sanity will reset for the final time in the fight, meaning you need to make use of Shards of Sanity from killing Adaptive Membrane shields that apply to both friendlies and enemies. The Synthesis Growths are in similar locations as the heroic difficulty, with the right side being much more grouped up than the left side. The raid will need to be split into 2 groups and DPS should balance out their cooldowns on the various Synthesis Growths in such a way that both sides finish at roughly the same time. The Regenerative Expulsion cast from the Mycelial Cysts on the floor only happens after the cysts have been targeted – imagine each of the cysts has an internal timer of 15 – 20 seconds until they begin their Regenerative Expulsion cast once a damage event has hit them, giving you a small window of time before the floor is pulsing with heavy AoE damage. To counter this, you can stay stacked up as a group to avoid cleaving any future Mycelial Cysts so they won’t be casting Regenerative Expulsion while you’re killing the Synthesis Growths near them. Don’t stand in the Mycelial Cysts for long periods of time, kill the Synthesis Growths as quickly as possible, spread out when you have Madness Bomb, and collect Shard of Sanity as a group to maximize your groups sanity during the phase. The small intermission once each side has been cleared is removed on Mythic difficulty, and instead the boss will immediately run to begin Phase 3.
Phase 3: Each Eternal Darkness cast will leave a giant pool of darkness on the ground that grows from a targeted players position. You should plan on getting at least 4 Eternal Darkness casts, likely 5, and will need some sort of movement speed effect like a Warlock Gateway, Wind Rush Totem, or Speed Potions for each of the casts. There are also 3 Insanity Bomb casts in this phase, each roughly 1 minute apart from each other, meaning you can use Tremor Totem on each cast. You can have preset spread positions so you don’t accidentally cleave other people, maximizing the amount of Sanity you have in the phase. After each movement at least 3 tentacles will slam down near your position, so make sure you don’t get hit by these, especially if you’re trying to stand in the pool of darkness to break your Adaptive Membrane shield. In addition to the boss’s Adaptive Membrane, 3 players will also be affected – they will need to run into the previous pool of darkness created from Eternal Darkness in order to break the shield, and a Shard of Sanity will come out of each player who breaks the shield – note: the sanity orb will travel in the direction you’re facing, so make sure you’re facing the boss.
A pretty normal talent setup works well for this fight. Ancestral Vigor can be helpful in both Phase 2 and Phase 3, so use it if you feel you need the extra health during high moments of damage. Wind Rush Totem is very strong on this fight for the last phase, as you will likely use some sort of movement mechanic (i.e. Wind Rush Totem, a Warlock Gateway, or Speed Potions each time the boss casts Eternal Darkness.
Notable Azerite Traits and Essences
Phase 3 will require some burst healing each time Eternal Darkness is cast, so having at least 1 Spouting Spirits is very helpful during this phase. Other standard traits like Overflowing Shores and Heart of Darkness do well on this fight. I would recommend playing fairly standard essences such as the Vision of Perfection major.
- Phase 1 has relatively low damage, but make sure you can see who the Gaze of Madness is channelling on as those players will take heavy damage if it is not interrupted.
- Interrupt the Gaze of Madness as soon as the channel of Breed Madness has begun – NOT the cast of the ability.
- You can be very lenient with your sanity in Phase 1 and have access to your on-use cloak effect to save you if you’re in trouble, or use it as a ‘teleport’ to the back of the room.
- Earth Elemental can be used to try and aggro some of the Nightmare Antigen adds to prevent your tanks from building up so many stacks of Nightmare Antibody.
- The fears from Madness Bomb and Insanity Bomb can be dispelled using Tremor Totem. In Phase 3, Tremor Totem will be available for every Insanity Bomb so make sure to use it.
- As stated above, Wind Rush Totem is invaluable for your group during some of the movement in Phase 3 so make sure you know when your team wants to use it. Generally, the movement is as follows for each Eternal Darkness: Warlock Gateway, Wind Rush Totem, Speed Potions, Warlock Gateway, and then Wind Rush Totem if you need to move one last time.
- Any time you are able to break your Adaptive Membrane shield you will spawn a sanity orb that will travel in front of your character – make sure you’re facing towards your group, especially in Phase 3 if you get this mechanic.
- Many players opt to use a Mouseover focus macro for warlock gateways on this fight. Below is a quick “How to” in order to properly set this up.
2) Bind it to something you can easily press. You can test that this is working my making sure you gain a focus target.
3) Go to the Game Menu (escape) -> Key Bindings -> Targeting -> Interact with mouseover. Make sure to bind this; you can test to make sure it is working by using your focus mouseover macro you just setup (you should gain a focus target) and then use your Interact with mouseover bind while hovering over your focus frame. If you gain a target, it is working properly and will allow you to use a warlock gateway without having to repeatedly click on it if multiple people are on top of it.