This is the first boss in The Venomous Abyss raid.  Nek'zali the Soulcoiler has two phases of mechanics with an intermission in between. Much of this fight interacts with the Soulcoil Well in the middle of the arena. If a player dies within the Soulcoil Well or a Raised Amani add reaches it, the boss becomes empowered, making the fight much more difficult. Keep away from the well at all times! 

Phase 1

• Bloodlust on pull or in Phase 2.

• Pull boss near the well.

• Essence rend: blue arrow over your head - move to outside edge to drop puddles.

• Tank: Possession Barrage - targeted tank runs away - spirits hit for raid-wide damage, reduced by travel distance.

• Raised Amani adds - slow/stun/grip.  Break shields to stop them moving to the centre, AoE.

Intermission (50%)

• Boss jumps to well and summons two large adds.  Kill one at a time to reactivate boss.

• Hungering Pyre - red group soak (half the raid).

• Those who didn't soak get small red circles.  spread. (On HEROIC they need to be placed on top of dead Amani adds)

Phase 2

• Similar to P1 plus:

• Invoke - raid wide damage and puddles start moving around the room randomly.

• Kill the boss before she gets to full energy.

Visual aid: https://raidplan.io/plan/ysk7ekhwzkb9vz3z