The Mythic version of this fight empowers Gurtogg's Bloodboil ability and Dia's Mark of the Necromancer ability. The strategy for completing the fight does not change, but players must work around the additional mechanics.
Bloodboil, in a reference to the original Gurtogg Bloodboil fight from the Black Temple raid, is now a DoT effect that can stack.
Bloodboil targets the five furthest away players from Gurtogg
The DoT effect lasts for 24 seconds, and Gurtogg will cast it every 8 seconds
The raid should form two five-person groups of ranged DPS/healers to soak Bloodboil
The first group should start the fight at a designated Bloodboil-soaking location and take three stacks before moving closer to the boss
When the first group reaches three stacks, the second group should move out to take the first group's place
These groups of players must be farther away from Gurtogg than the Dia Darkwhisper tank is, or else that tank will gain unhealable stacks of Bloodboil
Members of the current soak group who gain Mark of the Necromancer should use personal survivability CDs
It is very important that players in the soak group who are also affected by Mark of the Necromancer do not drop their Reap on the Bloodboil-soaking location. Minimizing the amount of movement the soak groups must do will help to insure that the Dia tank does not gain Bloodboil stacks.
Additionally, Mark of the Necromancer becomes more dangerous when dispelled.
Dispelling Mark of the Necromancer will deal Burden of the Necromancer damage to the entire raid for each player dispelled
Additionally, dispelling Mark of the Necromancer causes the debuff to jump to three targets instead of two
Healers must dispel strategically to prevent the raid from becoming overrun by Mark of the Necromancer debuffs or Burden of the Necromancer damage
It appears that Revival will not dispel the Mark of the Necromancer effect, leaving Mistweavers safe to use this ability at any time, and especially during the final 30% of the encounter
The raid should save as many raid-wide damage-reduction and healing CDs as possible for Dia's final 30%, as the damage from managing the Mark of the Necromancer debuff will be extremely high. The raid should stack in melee at this time since Reap no longer occurs.
Finally, during Dia's Wailing Horror/ Darkness ability, two Wailing Horrors will cross the room at any one time, rather than just one. Players must be more careful when dodging out of their paths, as the damage dealt by intercepting a Wailing Horror is very high.
Killing Gurtogg first, and quickly, is still the primary objective of the encounter. Fel Rage must be used well to maximize damage on Gurtogg.