The first iteration of the immortal council was not put into use because their ideals were too extreme. With the enemy at the gate, Lihuvim has little choice but to reactivate these dangerous prototypes.
This is a 3 phase encounter with 2 bosses in Phase 1 & 2 and all 4 bosses in Phase 3.
Phase 1: You will fight the Prototype of War (Necrolord) and the Prototype of Dury (Kyrian). When one of these bosses hit 50% they will retreat and Phase 2 will begin.
Phase 2: You will fight the Prototype of Absolution (Venthyr) and the Prototype of Renewal (Night Fae). When one of these bosses hit 50% they will retreat and Phase 3 will begin.
Phase 3: You will fight all 4 bosses. They will come back into the boss room on the same health they left on.
[Heroic/Mythic] You must defeat all 4 bosses within 20 seconds of each other else they will heal back up.
Necrotic Ritual - 4 Necrotic Ritualists spawn in set locations. Defeat them before they fill the room with 
Necrosis.
Windswept Wings - Push against the winds. Avoid the spears. Free people who get hit by the spears.
Hand of Destruction - Grips the entire raid to his location and places 
Sinful Projection on a majority of the raid.
Sinful Projection - After 4 seconds projectiles will shoot out from your front, back and sides. If you are hit by any you will take a burst of Shadow damage, be stunned for 2 seconds and have an additional stack of 
Burden of Sin.
Wild Stempede, - Watch out for the lines of beasts. They spawn from the edges of the room and go from one side to the other.
Withering Seeds - Prevent the seeds from dying. Heal them up to full one at a time to maintain a +Healing buff on the raid.
Animastorm - Tornadoes will spawn around the boss and swirl out from their body. Standing inside the tornado will deal Nature Damage and Silence the player.
In this phase all of the bosses will be active at the same time. Only worry about interrupting 
Gloom Bolt as it's more deadly than 
Anima Bolt.
Focus on priority mechanics as they come up. Necrotic Ritualists, Necrotic Ritual & 
Runecarver's Deathtouch should be dealt with instantly when they happen.
[Heroic/Mythic] When any boss reaches 0 Health it will start a 20 second cast to heal back to 100%. Defeat all 4 bosses within this time frame to beat the encounter.
Prototype of Duty Swing Timer: 1.5s (Curse of Weakness 1.8s)
Prototype of Absolution Swing Timer: 2s (Curse of Weakness 2.4s)
Raid damage dealt by 
Humbling Strikes is based on damage taken. Using 
Celestial Brew before the hit will lower this damage significantly.
Taunting Prototype of War / Renewal after they have been interrupted will help to get them into position as they like to chain cast and stand still.
Raid damage dealt by Humbling Strikes is based on damage taken. Using Fiery Brand before the hit will lower this damage by a large amount.
Focus your 
Avenger's Shields on Prototype of War to interrupt as many Gloom Bolts as possible.
Should your raid need it, Talenting into 
Hand of the Protector and throwing a 
Word of Glory on a Low Health seed will heal for a lot.
Divine Shield & 
Blessing of Protection can be used to remove stacks of Humbling Strikes.
Blessing of Protection can be used to free people stunned by spears.
Divine Shield & 
Blessing of Spellwarding can be used to negate stacks of 
Wracking Pain.
Spell Reflection can be used to reflect Gloom Bolt & Anima Bolt.
You can deflect the stun from Sinful Projection with Spell Reflection.
Rallying Cry is best used to help keep the raid healthy after Hand of Destruction.
Raid damage dealt by Humbling Strikes is based on damage taken. Using 
Barkskin / 
Survival Instincts will lower this damage by a large amount.
Stampeding Roar is useful to get players spread out after Hand of Destruction.
Anti-Magic Shell can be used to prevent stacks of Wracking Pain being applied.
Death's Advance can be used to negate the pushback effect of Windswept Wings.
If you get stunned by a spear or Sinful Projection, 
Icebound Fortitude will break the stun.
This is a 3 phase encounter with 2 bosses in Phase 1 & 2 and all 4 bosses in Phase 3.
Phase 1: You will fight the Prototype of War (Necrolord) and the Prototype of Dury (Kyrian). When one of these bosses hit 50% they will retreat and Phase 2 will begin.
Phase 2: You will fight the Prototype of Absolution (Venthyr) and the Prototype of Renewal (Night Fae). When one of these bosses hit 50% they will retreat and Phase 3 will begin.
Phase 3: You will fight all 4 bosses. They will come back into the boss room on the same health they left on.
[Heroic/Mythic] You must defeat all 4 bosses within 20 seconds of each other else they will heal back up.
Bloodlust/Time Warp/Heroism is best used in Phase 3 when all bosses are together. You should aim to hold DPS cooldowns for this point in the fight during Phase 2.
You should have pre-assigned locations for people during Necrotic Ritual to deal with the adds quickly.
Bosses during this mechanic should either be tanked on Triangle or Circle meaning that melee cleave from the add to the boss and ranged have to pre-move to their adds.
It's absolutely vital that you interrupt as many Gloom Bolt casts as possible. I would recommend setting up an interrupt rotation for this and using a Weak Aura (link) to manage this,
For this weakaura to function you will need to set up an MRT note similar to the below:
The above example is written in a way so that the boss is marked with a Square and each set of brackets indicates one interrupt. I've purposely overassigned with 1 ranged & 1 melee in each interrupt to cover scenarios where the raid is spread.
If you have a Protection Paladin they should set the Prototype of War as their focus target and just get loads of free interrupts with Avenger's Shield.
Gloom Bolt - The boss will target a random player and deal a burst of Shadow damage and apply a healing absorb. Make sure this is interrupted as much as possible.
Necrotic Ritual - 4 Necrotic Ritualists spawn in set locations. Defeat them before they fill the room with Necrosis.
Runecarver's Deathtouch - Two players will receive this debuff and must move into the 
Bastion's Ward shields and get dispelled.
Bastion's Ward - Barriers will be placed in the room which allow you to remove Runecarver's Deathtouch when the player is dispelled inside. Once a player has been dispelled the Barrier will be consumed.
Humbling Strikes - Swap on 1 stack. Deals damage to the raid based on damage taken.
If the raid is looking low before this, call for Healthstones/Potions/Personals.
Windswept Wings - Push against the winds and avoid being hit by the spears. If a player is hit by a spear they will be stunned and the raid will need to kill the spear to break them out.
People can be freed from the stun from the spear with Stun Immunities such as Icebound Fortitude and Blessing of Protection.
Hand of Destruction - Grips the entire raid to his location and places Sinful Projection on a majority of the raid.
Sinful Projection - After 4 seconds projectiles will shoot out from your front, back and sides. If you are hit by any you will take a burst of Shadow damage, be stunned for 2 seconds and have an additional stack of Burden of Sin.
Wracking Pain - Swap per stack. Point this away from the raid.
Burden of Sin - Applies every 2 minutes and every time you are hit by Sinful Projection.
Anima Bolt - The boss will target a random player and deal a burst of Nature damage and DoT to them. Make sure this is interrupted as much as possible.
Wild Stempede, - Watch out for the lines of beasts. They spawn from the edges of the room and go from one side to the other. There are fairly good sized gaps between the beasts, so wait for a gap and move through. If you are hit by a beast you will be knocked back and take a burst of damage.
Withering Seeds - Prevent the seeds from dying. Heal them up to full one at a time. 
Invigorating Bloom triggers when they are healed to full which heals the raid and applies a +healing buff.
Invigorating Bloom stacks up to 4 times and refreshes in duration when a new seed is healed to full. Make sure you do not let this buff expire as it makes healing the raid significantly easier.
Animastorm - Tornadoes will spawn around the boss and swirl out from their body. Standing inside the tornado will deal Nature Damage and Silence the player.
Note for tanks: After 3 tornadoes spawn, move the boss to give the raid space around the boss that is safe. The Hand of Destruction will happen shortly after the fourth tornado comes out so this makes it so that the raid does not get gripped through tornadoes.
In this phase all of the bosses will be active at the same time. Only worry about interrupting Gloom Bolt as it's more deadly than Anima Bolt.
Focus on priority mechanics as they come up. Necrotic Ritualists, Necrotic Ritual & Runecarver's Deathtouch should be dealt with instantly when they happen.
[Heroic/Mythic] When any boss reaches 0 Health it will start a 20 second cast to heal back to 100%. Defeat all 4 bosses within this time frame to beat the encounter.
Prototype of Duty Swing Timer: 1.5s (Curse of Weakness 1.8s)
Prototype of Absolution Swing Timer: 2s (Curse of Weakness 2.4s)
Raid damage dealt by Humbling Strikes is based on damage taken. Using Celestial Brew before the hit will lower this damage significantly.
Taunting Prototype of War / Renewal after they have been interrupted will help to get them into position as they like to chain cast and stand still.
Raid damage dealt by Humbling Strikes is based on damage taken. Using Fiery Brand before the hit will lower this damage by a large amount.
Focus your Avenger's Shields on Prototype of War to interrupt as many Gloom Bolts as possible.
Should your raid need it, Talenting into Hand of the Protector and throwing a Word of Glory on a Low Health seed will heal for a lot.
Divine Shield & Blessing of Protection can be used to remove stacks of Humbling Strikes.
Blessing of Protection can be used to free people stunned by spears.
Divine Shield & Blessing of Spellwarding can be used to negate stacks of Wracking Pain.
Spell Reflection can be used to reflect Gloom Bolt & Anima Bolt.
You can deflect the stun from Sinful Projection with Spell Reflection.
Rallying Cry is best used to help keep the raid healthy after Hand of Destruction.
Raid damage dealt by Humbling Strikes is based on damage taken. Using Barkskin / Survival Instincts will lower this damage by a large amount.
Stampeding Roar is useful to get players spread out after Hand of Destruction.
Anti-Magic Shell can be used to prevent stacks of Wracking Pain being applied.
Death's Advance can be used to negate the pushback effect of Windswept Wings.
If you get stunned by a spear or Sinful Projection. Icebound Fortitude will break the stun.
There are two key changes for Mythic:
All Necrotic Ritualists & Withering Seeds will be protected by 
Imprinted Safeguards reducing your effectiveness on them by 50%. These can be removed with another new mechanic 
Night Hunter.
Additionally the damage reduction provided by Bastion's Ward is reduced to 75% (down from 100%).
In addition to the assignments for Heroic (Interrupts & Kicks) you will need to assign where the four Night Hunters go. Their positions should be roughly similar to your Ritualists positions, however you will need to adapt as it's not always a clean split of 2 Melee & 2 Ranged.
I would recommend using a WeakAura to help manage this as we found this helpful during our PTR testing.
You should ideally have a rotation of speed boosts to help the raid move around quickly with Night Hunters.
It's also very important to keep the healing buff from Withering Seeds active in Phase 2 & 3. I would recommend assigning 1 or 2 healers to focus on managing this to ensure the healing buff does not drop.
This section will be updated once the boss has been defeated on Live Servers.
The big change for this fight are the Imprinted Safeguards and Night Hunters.
To manage this, simply have the raid in a position where they can move quickly to their designated locations to break the shields. Example footage below:
In terms of strategy for the encounter this does not change all too much from Heroic. You will need to be more mindful of timings of Necrotic Ritualists & Withering Seeds to pre-move and make sure that Night Hunter lines do not miss.