On Mythic difficulty, the Latent Energy debuff has no duration, and can only be removed by entering the Shadow Realm.
Soul Cleave will now send up to five players into the Shadow Realm, rather than solely the current tank
All players affected by Soul Cleave will take heavy Shadow damage from the attack, but only the tank is debuffed with Cloven Soul
Players must be within five yards of the tank in order to be sent down into the Shadow Realm; there is a small graphic that illustrates the range of the Soul Cleave effect
As in Heroic difficulty, players returning from the Shadow Realm will emit Wake of Destruction as they reappear in the Mortal Realm.
With a fixed raid size of 20 players, Zakuun will summon four Rumbling Fissures in each set, and players must soak three of them to prevent extra Fel Crystals from spawning
For the first two Rumbling Fissures casts, the off-tank should soak one of the three Rumbling Fissure spawns, and then taunt Zakuun before Soul Cleave
The tank without Latent Energy should move away to avoid being affected by Soul Cleave
The non-tank players with Latent Energy should stack on the current tank during the Soul Cleave cast, and use personal cooldowns to survive the Soul Cleave damage
While in the Shadow Realm, these players must dodge the Wake of Destruction and Ring of Destruction casts from Residual Energy spheres
All players in the Shadow Realm will take heavy damage if any player is struck by one of these effects, as it will trigger that player's Unleashed Energy
It is possible to collide with your own Wake of Destruction waves if you are moving as they spawn, so for the few seconds after Disembodied fades, these players should stand still
Additionally, those players who entered the Shadow Realm with Latent Energy will be affected by Exhausted Soul, rendering them unable to soak a Rumbling Fissure for the next 2.5 minutes. (Note that players affected by Exhausted Soul can still intercept Wake of Destruction waves.) The raid must assign three or four groups of players to soak Rumbling Fissures, then take the Soul Cleave, during the Armed phases.
The first Shadow Realm phase is the simplest, with only one Residual Energy present for players to dodge. Subsequent Shadow Realm phases are progressively more difficult, as each player who enters the Shadow Realm creates a Residual Energy in their location as they leave.
Each tank is only able to soak a Rumbling Fissure once, since Exhausted Soul lasts 2.5 minutes, meaning the first tank to soak will still have the Exhausted Soul debuff during the fourth set of Rumbling Fissures
For the first two Soul Cleaves, the raid can send only 3 players down - the tank who has soaked, and two non-tank players who soaked
The first group has only one Residual Energy to dodge
The second group will have four Residual Energies to dodge
During the second Armed phase, the tanks can no longer soak Residual Fissures, so 4 players total will be sent into the Shadow Realm
The third group will have seven Residual Energies to dodge
The fourth group (if used) will have eleven Residual Energies to dodge
Assign players with immunities or very strong personal CDs to the fourth Soul Cleave
Once Fel Lord Zakuun enters his Enrage phase and stops casting Soul Cleave, any players who gain Latent Energy will not be able to clear the debuff, and will be unable to soak any further Rumbling Fissures or intercept any Wake of Destruction waves to prevent them from colliding with Fel Crystals.
This puts a soft Enrage on the encounter, since eventually every player in the raid will have Latent Energy, and it will be impossible to prevent Wake of Destruction waves from colliding with Fel Crystals and triggering Unleashed Energy. Realistically, the fight will become very difficult well before the raid reaches 100% Latent Energy saturation, so it is important not to skip sending players down into the Soul Cleave, even though doing so makes subsequent Shadow Realm phases more challenging.
Finally, in Mythic difficulty, Fel Lord Zakuun's Cavitation casts during the Armed and Enrage phases will summon 8 Wake of Destruction projectiles, rather than 4.