For countless ages, Sire Denathrius stood among the Eternal Ones who rule the realms of Death. But in the Shadowlands' darkest hour, he has betrayed his sacred duty. With his bloodthirsty living blade Remornia at his side and defended by his most sycophantic loyalists, Denathrius will cut a swath through any who stand against him and cast their remains into the inescapable terror of the Maw.
Phase 1
Swap after each 
Cleansing Pain hit
When the boss reaches 100 energy, move him out of 
Command: Ravage
Intermission
Your movement speed is based on the amount of 
Burden of Sin you still have. Each stack reduces your movement speed by 20% and silences you.
Reach the middle of the room to have all stacks removed and survive the fall into Phase 2.
Phase 2
One tank takes Sire Denathrius, the other takes Remornia
Swap after each Wracking Pain cast, avoid getting multiple stacks of this.
If tanking Sire Denathirus point him towards adds so they get the damage taken increase on them.
When any add dies they will fire 
Cresendo projectiles into the room. If you are hit by any of these you will be knocked back.
Move out of 
Hand of Destruction. Damage taken is based on your distance from it. You can use the mirrors on the edge of the room in this phase to make it easy.
When Sire Denathirus is at 100 energy he will do Command: Massacre. Dodge these swords!
Phase 3
It's only Sire Denathirus now. The side of the room is now dangerous.
Swap on 4-6 
Scorn stacks.
Move out of Hand of Destruction. Damage taken is based on your distance from it.
When he reaches 100 energy he will do the 100 energy abilities from Phase 1 + 2 
Ravage + 
Massacre
Celestial Brew should be active for each 
Blood Price to ensure you are on full health after.
Ideally you should be the tank assigned to the second Cleansing Pain as you can pre-place your 
Transcendence before Blood Price and teleport back in place after he has thrown you. If this is done correctly the boss will not move.
During the Intermission Phase once you have reached the middle and cleared your stacks of Burden of Sin, you can place 
Tiger's Lust on another player to help them out.
In Phase 2 + 3 have Transcendence on the main boss platform, there are many mechanics that can knock you back, be ready to react if you get knocked badly.
If you dodge Remornia's melee swings, you will not have a stack of 
Carnage applied.
If you dodge Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can use 
Infernal Strike to counter the knockback from 
Shattering Pain (if you are not in position with the raid).
If you dodge Remornia's melee swings, you will not have a stack of Carnage applied.
If you dodge Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can cast Blessing of Freedom on yourself or another when the boss teleports at the end of Phase 1 to trigger the intermission to negate most of the movement speed reduction from 
March of the Penitent.
If you have 
Blessing of Spellwarding or 
Divine Shield active during Wracking Pain the debuff will not be applied.
In Phase 2 + 3 if you find yourself in a situation where you will get knocked back badly (Phase 2 - Heroic: Cresendo, Phase 3: Shattering Pain) you can use Divine Shield to negate the knockback.
If you parry Remornia's melee swings, you will not have a stack of Carnage applied.
If you parry Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can reflect the damage from Hand of Destruction and Inevitable back to the boss with 
Spell Reflection.
Intervene can be used on your co-tank to mitigate some of their damage taken whilst you are not tanking.
You can use 
Heroic Leap to counter the knockback from Shattering Pain (if you are not in position with the raid).
Rallying Cry will likely be used during Blood Price / Cleansing Pain (Phase 1), and Hand of Destruction (Phase 2 + 3).
If you parry Remornia's melee swings, you will not have a stack of Carnage applied.
If you parry Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can cast 
Stampeding Roar when the boss teleports at the end of Phase 1 to trigger the intermission to speed boost the entire raid for March of the Penitent!
If you dodge Remornia's melee swings, you will not have a stack of Carnage applied.
If you dodge Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
Anti-Magic Zone is great to use to mitigate damage from Cleansing Pain (Phase 1), and Hand of Destruction (Phase 2 + 3).
You can cast 
Death's Advance when the boss teleports at the end of Phase 1 to trigger the intermission to negate most of the movement speed reduction from March of the Penitent.
The passive effect of Death's Advance means that you do not need to remove any stacks in Phase 1 to survive the intermission.
If you have 
Anti-Magic Shell active during Wracking Pain the debuff will not be applied.
In Phase 2 + 3 if you find yourself in a situation where you will get knocked back badly (Phase 2 - Heroic: Cresendo, Phase 3: Shattering Pain) you can use Death's Advance to negate the knockback.
If you parry Remornia's melee swings, you will not have a stack of Carnage applied.
If you parry Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
Please note: This fight was tested once, and this was a very limited test with quite a few issues. Therefore a lot of the information in this page is speculative and footage is missing for a majority of mechanics. This page will be updated once the raid goes live.
This section of the fight has three distinct stages, as when Sire Denathrius reaches 100 energy one third of the room will be covered in 
Desolation via Command: Ravage.
Burden of Sin - At the start of the encounter everyone in the raid will have 4 stacks of this debuff. This deals a relatively low amount of Shadow damage, however has interactions with Blood Price, Cleansing Pain and the Intermission ability March of the Penitent. How it interacts with these abilities will be explained in the sections for those abilities.
[Heroic] Burden of Sin - You will now have 5 stacks of Burden of Sin. This means that if you do not cleanse any stacks in Phase 1 you will be unable to move and die during the Intermission phase.
Blood Price - At the start of each section this ability will be cast. When cast it will stun all players in the raid for 3.5 seconds and for each player that shares the same amount of Burden of Sin stack as you, you will take a small burst of Shadow damage.
Example: if 15 people have 5 stacks, 5 have 4 stacks. The players with 5 stacks will take 3x the damage as the players with 4 stacks as there will be 15 sets of damage rather than 5. You will want the raid to have a somewhat balanced amount of stacks to ensure that damage/healing required is consistent. At the start of the encounter you will need to use Mitigation cooldowns as there is a large inevitable overlap of stacks.
Cleansing Pain - Twice in each section this ability will be cast towards the current tank. Any player in the very large cone in front of Sire Denathrius will be hit and lose 1 Burden of Sin stack. For each Burden of Sin stack that was lost an Echo of Sin add will spawn. These Echo of Sin adds will repeatedly cast 
Painful Memories dealing a small amount of raid wide Shadow damage, however as you will be spawning many of these at a time it becomes a large amount of raid wide Shadow damage.
The raid should aim to be split into two groups, with each group taking turns being hit by this mechanic so you end the phase on 2 stacks.
Inevitable - If the tank is ever not in melee range of Sire Denathrius he will teleport to their location and hit the tank for 50% Weapon Damage (whatever that's meant to mean?)
Feeding Time - Sire Denathrius will mark two non-tank players and after 5 seconds will hit them and any player within 4 yards of them. Sire Denathrius will heal for 150% of the damage dealt.
[Heroic] 
Night Hunter - This replaces Feeding Time. This is similar to the mechanic it replaced however there is now an add that will charge at the player after 6 seconds. The damage dealt by this add is very high and can be reduced by players being hit by the charge from the add. Players cannot be hit by multiple in a short period of time as when they are hit by one they will receive the 
Touch of the Night debuff.
When Sire Denathrius reaches 70% health the Intermission will begin.
When this phase begins all players will be knocked to the edge of the room and Sire Denathrius will begin to cast March of the Penitent for 15 seconds.
For each Burden of Sin stack that you have, your movement speed will be slowed by 20% and you will be unable to cast any abilities.
Moving within 16 yards of Sire Denathrius will remove all Burden of Sin stacks from you.
If you have any Burden of Sin stacks when this ability finishes casting you will die.
It is to pre-cast movement speed restricting abilities and negate the slow from March of the Penitent. These would be abilities such as Death's Advance, 
Ghost Wolf, 
Blessing of Freedom.
If you have more than two stacks of Burden of Sin when going into this phase, it is very likely you will not reach Sire Denathrius in time and die.
You will now be in a new room. This room has a central square, 4 paths each with Mirrors at the end and 4 side platforms.
The Mirrors will teleport you to the other side of the encounter area when you walk through them. It is advisable to tank the bosses near a mirror to allow you to move long distances quickly as required from Hand of Destruction.
Remornia
During this phase the sword Remornia will be an active boss and will share health with Sire Denathrius. Any damage taken by Remornia will be dealt to Sire Denathrius with 
Bloodbound. Remornia will also teleport to tanks if they are out of range with Inevitable.
Aim to position Remornia near Sire Denathrius for more raid DPS.
Carnage - This is the main tank mechanic of this phase from Remornia. This ability is cast every ~15 seconds and applies a stacking bleed to the tank.
Impale - Several players will be marked by Remornia and shortly after this the blade will charge at them dealing a large amount of Physical damage. Any players in the path of these players will also be hit by this mechanic. Anyone hit will have the Carnage bleed applied to them.
Sire Denathrius
Wracking Pain - This is the main tank mechanic of this phase from Sire Denathrius. This ability is cast every ~20 seconds and will deal a large amount of Shadow damage to the tank and increase their damage taken by 30% for 24 seconds.
This will also increase the damage taken by the Crimson Cabalists.
[Heroic] Wracking Pain increases damage taken by 50% (up from 30%).
Hand of Destruction - Sire Denathrius will pull all players to his location and create an image of himself. After 6 seconds this image will detonate dealing a large amount of Shadow damage to the raid. This damage is reduced based on your distance from the boss.
Command: Massacre - When Sire Denathrius reaches 100 energy Massacre will be cast. Remornia will despawn and large swords will appear in the encounter space. Each of these swords will be targeting a player and slice in that direction. Avoid all of these swords!
Crimson Cabalist
These adds will spawn throughout the phase in waves of 4. They will spawn on the main platform and on the side platforms. They will channel 
Crimson Chorus which deals raid wide Shadow damage.
Throughout testing, these adds seemed to always spawn relative to boss position. 2 on the main platform and 1 on each of the side platform nearby.
As the adds on the side platforms cannot be accessed by melee DPS, they will need to be focused down by ranged DPS.
Note: Some melee specs can access the side platforms with leap abilities such as 
Glide, Heroic Leap, 
Shadowstep, and the Venthyr ability 
Door of Shadows. However it is important to note that you also need to get back to the main platform.
Cresendo - When any add dies it will fire a volley of these projectiles into the room. If you are hit by any of these you will be knocked back and can potentially fall off and die.
When Sire Denathrius reaches 40% Phase 3 will begin.
At the start of this phase Sire Denathrius casts 
Indignation which disables all mirrors and a ring around the outer edge of the room forms. If you step into this ring you will take a large amounf of Shadow damage every second.
Remornia is now wielded by Sire Denathrius. He will deal 50% more damage, apply Scorn on his hits and attack 25% slower. Scorn is the primary tank mechanic of this phase.
Fatal Finesse - Several players will be marked with this debuff. After 5 seconds they will deal a moderate amount of Shadow damage to all players within 9 yards and apply a DoT for 20 seconds dealing a low amount of Shadow damage.
[Heroic] An orb will spawn from each of the areas which will need to be soaked else the group will take a large burst of damage.
Hand of Destruction - This is the same as it was in Phase 2, but you no longer have access to mirrors so will need to run away from the boss.
Shattering Pain - Sire Denathrius will attack the tank for 100% Weapon Damage (again not sure how much this is?) 3 times and then deal raid wide Shadow damage and knock all players away.
Sinister Reflection - When Sire Denathrius reaches 100 energy he will spawn a clone of himself that replicates one of his previous 100 energy abilities: Ravage and Massacre.
Ravage - As with Phase 1 will leave an area of the encounter unusable. This will act as the soft-enrage of the encounter.
Massacre - This will force the raid to move around to dodge the swords. Will become more difficult with less space.
This boss received no testing on Mythic. This section will be updated once we have more information, as the raid received lots of changes since previous tests for every boss this section is risky to try to do for now.
Swing Timer: 2s (Curse of Weakness 2.4s)
Celestial Brew should be active for each Blood Price to ensure you are on full health after.
Ideally you should be the tank assigned to the second Cleansing Pain as you can pre-place your Transcendence before Blood Price and teleport back in place after he has thrown you. If this is done correctly the boss will not move.
During the Intermission Phase once you have reached the middle and cleared your stacks of Burden of Sin, you can place Tiger's Lust on another player to help them out.
In Phase 2 + 3 have Transcendence on the main boss platform, there are many mechanics that can knock you back, be ready to react if you get knocked badly.
If you dodge Remornia's melee swings, you will not have a stack of Carnage applied.
If you dodge Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can use Infernal Strike to counter the knockback from Shattering Pain (if you are not in position with the raid).
If you dodge Remornia's melee swings, you will not have a stack of Carnage applied.
If you dodge Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can cast Blessing of Freedom on yourself or another when the boss teleports at the end of Phase 1 to trigger the intermission to negate most of the movement speed reduction from March of the Penitent.
If you have Blessing of Spellwarding or Divine Shield active during Wracking Pain the debuff will not be applied.
In Phase 2 + 3 if you find yourself in a situation where you will get knocked back badly (Phase 2 - Heroic: Cresendo, Phase 3: Shattering Pain) you can use Divine Shield to negate the knockback.
If you parry Remornia's melee swings, you will not have a stack of Carnage applied.
If you parry Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can reflect the damage from Hand of Destruction and Inevitable back to the boss with Spell Reflection.
Intervene can be used on your co-tank to mitigate some of their damage taken whilst you are not tanking.
You can use Heroic Leap to counter the knockback from Shattering Pain (if you are not in position with the raid).
Rallying Cry will likely be used during Blood Price / Cleansing Pain (Phase 1), and Hand of Destruction (Phase 2 + 3).
If you parry Remornia's melee swings, you will not have a stack of Carnage applied.
If you parry Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
You can cast Stampeding Roar when the boss teleports at the end of Phase 1 to trigger the intermission to speed boost the entire raid for March of the Penitent!
If you dodge Remornia's melee swings, you will not have a stack of Carnage applied.
If you dodge Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.
Anti-Magic Zone is great to use to mitigate damage from Cleansing Pain (Phase 1), and Hand of Destruction (Phase 2 + 3).
You can cast Death's Advance when the boss teleports at the end of Phase 1 to trigger the intermission to negate most of the movement speed reduction from March of the Penitent.
The passive effect of Death's Advance means that you do not need to remove any stacks in Phase 1 to survive the intermission.
If you have Anti-Magic Shell active during Wracking Pain the debuff will not be applied.
In Phase 2 + 3 if you find yourself in a situation where you will get knocked back badly (Phase 2 - Heroic: Cresendo, Phase 3: Shattering Pain) you can use Death's Advance to negate the knockback.
If you parry Remornia's melee swings, you will not have a stack of Carnage applied.
If you parry Sire Denathrius' melee swings in Phase 3, you will not have a stack of Scorn applied.