Soulrender Dormazain extracts anima from the hellaciously brutish captives of Torghast to fuel the Jailer's armies. The tormentor has never met a soul he couldn't break, but his latest victim is proving resistant to the usual methods. Feeding on this captive's unending rage, Dormazain will enjoy spending millennia finding his weaknesses.
Don't stand too close to Garrosh as you will be unable to damage or heal.
Swap at 1 stack of 
Ruinblade.
Avoid being hit by 
Torment. If you are the player calling out where to go for your group (or are in a no-comms PuG) look to the back of the room to see which area is safe.
When the boss is at 100 energy 
Tormented Eruptions will be cast which is Torment 5 times in a row.
Warmonger Shackles need to be snapped within 40 seconds of spawning. Each snap will deal high raid wide damage.
Watch out for players with 
Brand of Torment.
Interrupt every 
Agonizing Nova cast. Do not let any casts complete.
Both 
Clash and 
Ring of Peace work to move the Agonizers. Note: Clash will root the Agonizer for 4 seconds after it has moved.
If the Agonizers are grouped up 
Sigil of Silence or 
Sigil of Misery can be used to stop their casts.
Infernal Strike can be used to break a 
Warmonger Shackle if there is no Warlock Gateway to use.
Kyrian Demon Hunters should hold 
Elysian Decree for Agonizers as their spawns roughly line up with the cooldown.
[Mythic] 
Imprison should be used on one Agonizer each wave.
Blessing of Protection and 
Divine Shield can be used to remove the Ruinblade debuff.
Keep an eye out for Agonizing Nova casts that are close to being complete and rotate your 
Avenger's Shield targets as necessary to interrupt.
Ruinblade can be blocked.
Shockwave is good to use once the Agonizers have been grouped together to stop all of their casts and keep them still for easier AoE DPS.
Stampeding Roar is useful to help the raid get into position quickly during the Tormented Eruptions dance.
Anti-Magic Zone is best used when the raid is snapping Warmonger Shackles.
The large benefit of playing a Blood Death Knight on this encounter is the ability to grip the Agonizers together for efficient AoE. They will generally spawn with only 1 that is far away from the others, so if you grip that towards the others you can mass grip togther with 
Gorefiend's Grasp.
If you are a Necrolord you can rotate Gorefiend's Grasp and 
Abomination Limb on each add wave to grip them together every time making the DPS check on the encounter significantly easier for the raid.
This encounter is a one-phase fight where Soulrender Dormazain is torturing Garrosh. All mechanics are centred around this torture. The area outside of the arena is classed as the 
River of Souls, which renders you unable to damage or heal.
Ruinblade - This is the tank swap of the encounter, a relatively simple +100% Physical damage taken debuff.
Torment - One of the four quadrants of the room will slowly fill from the back of the room towards Garrosh with Torment. Any players inside will lethal burst of Shadow damage.
I would advise having four raid markers in the room as shown in the positions shown on the RaidPlan Map above. You will then need one player to keep an eye on the back of the room and call out the safe spot.
Tormented Eruptions - When Soulrender Dormazain is at 100 energy he will launch multiple waves of Torment in quick succession. There will be 5 in total.
During testing, it was observed that this dance phase always ended on the first safe spot.
Warmonger Shackles - Whilst shackled Garrosh will begin to cast 
Hellscream, to stop this cast all 3 Shackles will need to be snapped. Snapping a shackle hits the raid with a large burst of Shadow damage from 
Unleashed Tyranny.
[Heroic] 
Soul Manacles - Any player who snaps a Shackle will have this DoT placed on them for the rest of the encounter.
[Heroic] 
Rendered Soul - Periodically throughout the fight, fragments of Garrosh's Soul will impact on the floor. Avoid these to not take a large burst of Shadow damage.
Brand of Torment - Two players, will be marked with this and become 
Tormented. They will deal a moderate amount of Shadow damage to any players within their radius. However, they will also increase the damage taken by the Mawsworn Agonizers by 50% each.
Mawsworn Agonizer
These adds will spawn from the back of the room throughout the encounter and attempt to reach Garrosh. If they get too close to Garrosh (or reach 100 energy), they will gain 
Defiance, preventing them from being crowd controlled and increasing damage dealt by 200%.
Agonizing Nova - Is their only spell cast, and they will repeat this cast until they die. This cast can be interrupted, stopped with stuns etc. If any cast is successful, a large amount of Shadow damage will be dealt to everyone, and movement speed will be reduced by 20% (stacking).
Swing Timer: 1.5s (Curse of Weakness 1.8s)
Both Clash and Ring of Peace work to move the Agonizers. Note: Clash will root the Agonizer for 4 seconds after it has moved.
If the Agonizers are grouped up Sigil of Silence or Sigil of Misery can be used to stop their casts.
Infernal Strike can be used to break a Warmonger Shackle if there is no Warlock Gateway to use.
Kyrian Demon Hunters should hold Elysian Decree for Agonizers as their spawns roughly line up with the cooldown.
[Mythic] Imprison should be used on one Agonizer each wave.
Blessing of Protection and Divine Shield can be used to remove the Ruinblade debuff.
Keep an eye out for Agonizing Nova casts that are close to being complete and rotate your Avenger's Shield targets as necessary to interrupt.
Ruinblade can be blocked.
Shockwave is good to use once the Agonizers have been grouped together to stop all of their casts and keep them still for easier AoE DPS.
Stampeding Roar is useful to help the raid get into position quickly during the Tormented Eruptions dance.
Anti-Magic Zone is best used when the raid is snapping Warmonger Shackles.
The large benefit of playing a Blood Death Knight on this encounter is the ability to grip the Agonizers together for efficient AoE. They will generally spawn with only 1 that is far away from the others, so if you grip that towards the others you can mass grip togther with Gorefiend's Grasp.
If you are a Necrolord you can rotate Gorefiend's Grasp and Abomination Limb on each add wave to grip them together every time making the DPS check on the encounter significantly easier for the raid.