Essential abilities: Interrupts, Cleanse
Strategy:You don't fight the Manifestation of Lord Arak, just kill the Manifest Terror adds. Interrupt the Horrific Transformation. If you handle the interrupts correctly, this is a pretty easy fight.
Phase 1: Before the first Manifest Terror dies Mechanics: Manifest Terror Shadow Cleave: A cleave that deals 7.5k to tank, 12k to non-tanks
Numbing Cold: Interruptable debuff on all players. Cleansable, save interrupts for Horrific Transformation.
Nightmare Fracture: He will emote "Manifest Terror creates a fracture in reality!". A portal opens and spawns adds one at a time until the portal is closed.
Horrific Transformation: A blue glow will surround the Manifest Terror. This cast MUST be interrupted, or bad things happen. If the cast completes, the Manifest Terror will transform into a new add, heal back up to 100%, and gain new abilities. There are a few different types of adds.
Phase 2: Manifestation of Lord Arak Once the first Manifest Terror dies, your camera will focus on Lord Arak. Do not DPS Lord Arak, keep killing Manifest Terrors. Lord Arak will need to be kited by the tank, avoiding his mechanics.
Mechanics: Manifestation of Lord Arak Smash: This is a large red AoE around Lord Arak. Run out of this or take 50-60k damage and knockback.
Slash: A yellow cone AoE that follows the tank. When it stops, the tank needs to avoid the cleave. Deals 50-70k damage. Point away from the group.
Cirlce of Terror: Melee range AoE, deals 18k to tank, 30k to non-tanks.
If Horrific Transformation is NOT interrupted: Mechanics: Mage Manifest Terror Dark Water Bolt: This puts a red pulsing AoE on a random player before a water bolt shoots at them. It deals approximately 35k damage. LoS this using the middle area.
Raging Tide: A yellow rectangular AoE wave that goes out from the Mage Manifest Terror. Deals 10-15k damage and knockback.
Soul Anchor: A small water foothold that puts a blue beam on all players. Deals 4k damage every 3 seconds until the foothold is destroyed.
Mechanics: Turtle Manifest Terror Shell Shock: Stationary cast, aimed at the tank. When cast is complete, he does a short charge at the tank and generates a small yellow AoE burst dealing 60k to anyone nearby.
Double Dragon Turtle: 2 quick attacks to the tank, first one hits for 30-40k, and the second hits for 7.5k.
Toxic Spit: 30k ranged attack on the tank. Interruptable.
Mechanics: Sobek Manifest Terror Poisoned Spear: Hits the tank for 12k, and puts a DoT on that deals 1.2k every 2 seconds for 10 seconds.
* There are other abilities for the Sobek, but I have not seen them and do not have info on them. Will update when I do.
Tanks: * Interrupt Horrific Transformation
* Kite the Manifestation of Lord Arak
* Pick up all adds while kiting
* Make sure Slash is aimed away from the group
Healers: * Cleanse Numbing Cold
DPS: * Interrupt Horrific Transformation (VERY IMPORTANT)
* DPS Manifest Terrors as quickly as possible
* DPS Nightmare Fractures when they spawn
* Use a ranged spec if possible