
Abilities:
Phase 1:
Eruption - causes the ground to burst with slime - dealing a large amount of nature damage if hit
Decrepit Fever - Reduces maximum health reduced by 50% and deals nature damage every 3 seconds
Spell Disruption - Decreases casting speed by 300%
Phase 2:
Eruption - causes the ground to burst with slime - dealing a large amount of nature damage if hit
Palgue Cloud - Constantly deals large amount Nature damage to anyone within 21 yards
Strategy:
Phase 1:
Start the encounter by having the tank pull the boss and positioning him at (1) while having all of the ranged dps/healers move to where the boss was originaly standing (5).
 The Inital Pull
Heigan the Unclean will constantly cause the floor to errupt with slime except for 1/4th of the room. The area that is safe is predictable as shown in the chart below:
 Move from 1 to 2 to 3 to 4
 Then from 4 to 3 to 2 to 1
When Heigan causes and eruption in the floor the tank along with the melee dps will need to move to (2). Again after another eruption the melee group will need to move to (3), then (4), and then back to (3), (2), (1), (2), (3)... etc. There will be pauses inbetween each eruption for the DPS to go all out on the boss. Keep up this rotation until Heigan teleports to (5) which indicates the start of phase 2. Also be sure to cleanse Decrepit Fever especially on the tank.
Phase 2:
The start of phase 2 will begin when Heigan teleports to the platform (5) and starts dealing damage to anyone on this plateform - at this point the entire raid will need to move to 1 and then do the full rotation after each eruption. The eruptions will also be much faster the before - almost to the point where the raid will need to be moving non-stop. Eventually Heigan will leave the platform and run towards the highest threat player (probably the tank) and phase 1 will start again.
 Everyone Now! 1 to 2 to 3 to 4
 Then from 4 to 3 to 2 to 1
It is important to note that Heigan resets the safe spot to (1) everytime he changes phases - so the raid must be ready to move back to (1) no matter what position they were in during a phase change.
Video:

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