The Council of Blood presides over courtly functions in Revendreth. Castellan Niklaus is a strict military commander with an indomitable will and impenetrable armor. Lord Stavros, a foppish dandy, leads the court in dance but is also deadly with his blades. Baroness Frieda wields powerful anima magic and commands the dredger wait staff--along with the respect of the entire court.
Baroness Frieda
Ensure 
Dreadbolt Volley is interrupted.
If she is the last boss alive she will gain a new tank buster ability: 
Soul Spikes. Have cooldowns active for this to lower the amount of raid damage taken!
Lord Stavros
Ensure you are facing a wall, so that when he uses 
Evasive Lunge he charges into the wall. Swap at 2 stacks.
After 1 boss has been killed and Lord Stavros is still alive, he will summon dancers to the room periodically. Getting hit by them will stun you. When he is the last boss alive they will cover the entire room and only one will be attackable. Kill it and get to the safe spot!
Castellan Niklaus
Swap at 2 stacks of 
Duelist's Riposte
He will spawn a Dutiful Attendant which will channel the 
Unyielding Shield. This makes that boss immune. Kill that add!
If he is your final boss, ensure no adds are killed near the boss as when anything dies, everything in 12y gets the 
Castellan's Cadre buff.
Dance Phase/Intermission
When any boss reaches 50% health, an intermission will trigger. Find your spot on the dance floor or die!
If you kill Baronness Last, have 
Celestial Brew and/or 
Dampen Harm or 
Zen Meditation active for Soul Spikes.
Try to have Celestial Brew active for the 2nd stack of Evasive Lunge / Duelist's Riposte.
Remember to 
Touch of Death the bosses, you will get multiple uses of it during the encounter.
[Heroic] 
Tiger's Lust will clear stacks of 
Two Left Feet. Abilities such as 
Roll / 
Chi Torpedo will generate fewer stacks for a longer distance covered.
If you kill Baronness last, have 
Demon Spikes and/or 
Fiery Brand, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
If you kill Castellan Niklaus second or third utilise 
Sigil of Chains to bring Dredger Servants together for cleave DPS.
[Heroic] If you kill Lord Stavros last you can 
Infernal Strike to cover long distances and only gain one stack of Two Left Feet.
If you kill Baronness last, have 
Shield of the Righteous and/or 
Ardent Defender, 
Guardian of Ancient Kings, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
[Heroic] If you kill Lord Stavros last you can use 
Divine Shield or 
Blessing of Freedom to remove Two Left Feet.
You can reset the cooldown of your 
Taunt with 
Heroic Leap should you need multiple.
Evasive Lunge is blockable. Ensure 
Shield Block is active for each cast.
If you kill Baronness last, have Shield Block, 
Ignore Pain and/or 
Shield Wall, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
[Heroic] If you kill Lord Stavros last you can Heroic Leap to cover long distances and only gain one stack of Two Left Feet.
If you kill Baronness last, have 
Ironfur stacks and/or Barkskin, Survival Instincts, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
If you kill Lord Stavros last use 
Stampeding Roar to help the raid get in position for 
Dancing Fools.
[Heroic] If you kill Castellan Niklaus last you can use 
Soothe to remove 
Castellan's Fury.
[Heroic] If you kill Lord Stavros last you can use change form to remove Two Left Feet.
You have multiple taunts with 
Death Grip and 
Dark Command.
If you kill Baronness Last, have 
Icebound Fortitude, 
Vampiric Blood or an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte. You will also want to time a 
Death Strike after this hit as it will provide a large amount of healing.
If you kill Castellan Niklaus second or third utilise Death Grip / 
Gorefiend's Grasp to bring in Dredger Servants for cleave DPS.
During this encounter you have three bosses, however they do not share health and will heal back to full health when one has been killed. Therefore you should focus the bosses down one at a time.
Recommended Kill Order: Baronness Frieda > Castellan Niklaus > Lord Stavros (subject to change when raid goes live)
When any boss reaches 50% they will trigger the intermission phase..the 
Danse Macabre!
As you fight the bosses the raid will receive a stacking debuff 
Oppressive Atmosphere. This deals a relatively low amount of Shadow damage, however it stacks and the longer each phase lasts the more damage the entire raid will be taking. This debuff resets when you kill a boss or trigger an intermission.
As there are 3 bosses, it is advisable for one tank to have both Castellan Niklaus and Baroness Frieda and the other tank to hold Stavros.
Drain Essence - Every ~22 seconds this will be cast, targeting several random targets and dealing a moderate amount of Shadow damage every second for 4 seconds.
Dreadbolt Volley - This ability is cast repeatedly and if it is successful will apply a small amount of Shadow damage over 12 seconds to the entire raid. This cast can be interrupted and will require a 2/3 person interrupt rotation.
The below abilities will only be cast when other bosses have died.
Prideful Eruption - This ability is cast when at least 1 boss has been killed and Baronness Frieda is still alive. This will place a circle around each player in the raid and after a short period every player in the raid will take a large amount of Shadow damage. This damage is also dealt to players within 6 yards.
Soul Spikes - This ability is cast when Baronness Frieda is the last boss alive. This is the new tank mechanic for the end of the fight, the boss will send out 4 of these Spikes over a 4.5 second period. Each Spike deals a large amount of Physical damage, increases damage taken from further Spikes, and finally deals raid wide damage based on the amount of damage taken.
This cast is focused on the tank, therefore the tank will need to have cooldowns active to lower the amount of raid damage taken as much as possible. Use external cooldowns from healers should you not have any available! Only the tank with cooldowns should take this.
[Heroic] 
Twisted Pain - This ability is cast when Baronness Frieda is the last boss alive. When any player takes damage from an ability cast by the boss they will spawn a 
Manifest Pain pool underneath them which lasts for 1.5 minutes and deals a small amount of Shadow damage every 0.5s whilst standing in it.
Evasive Lunge - This is the primary tank mechanic for Lord Stavros for the encounter. When cast Lord Stavros will teleport behind the tank and charge through the tank and 20y more. Anyone hit by this ability will take a large burst of Physical damage and be left with a stacking debuff increasing damage taken by Evasive Lunge for 100% per stack.
Because Lord Stavros teleports behind the tank it is possible to position yourself in a way so that he charges off the side of the room and does not hit anyone else.
Dark Recital - This ability is frequently cast by Lord Stavros and pairs several players together with a red beam (this beam is only visible to the pair partners). These players will take damage every 0.5s they are further than 8y from their partner. Whilst they have this debuff they will be spawning small damaging zones under their feet, the players will simply need to keep moving for the duration of the debuff to not take any damage from this.
The below abilities will only be cast when other bosses have died.
Waltz of Blood - This ability is cast when at least 1 boss has been killed and Lord Stavros is still alive. A group of Waltzing Venthyr will appear in set locations of the dance floor and they will move around that area. Any player who is hit by any of these will be stunned for 1 second and take a moderate amount of Shadow damage.
Dancing Fools - This ability is cast when Lord Stavros is the last boss alive. All of the Waltzing Venthyr are called to the dance floor and cover the entire encounter space. You will need to move around their dancing to survive. Shortly after spawning they will start to cast 
Violent Uproar which will deal a lethal amount of damage to all players in 11 yards, however one of these adds will be attackable. Kill it before the cast ends and move to its location to survive.
[Heroic] Two Left Feet - This ability is cast when Lord Stavros is the last boss alive. Every time you move or jump your movement speed will be reduced by 2% every 0.3s. Standing still removes these stacks.
Abilities that remove movement impairing effects will reset the stacks of slow on a player so these should be used on players with high stacks that need to move, the ones observed to work are: Shapeshifting (Druid), Blessing of Freedom (Paladin), Divine Shield (Paladin), Tiger's Lust (Monk), 
Cloak of Shadows (Rogue), 
Ice Block (Mage), 
Dispersion (Shadow Priest), 
Vengeful Retreat (Havoc Demon Hunter), 
Master's Call (Hunter), 
Disengage (if talented for 
Posthaste - Hunter), 
Bladestorm (DPS Warrior), 
Avatar (Warrior), 
Demonic Circle: Teleport (Warlock).
Duelist's Riposte - This is the primary tank mechanic for Castellan Niklaus for the encounter. When cast this will deal a large burst of Physical damage to the tank and leave a stacking debuff increasing damage taken from Duelist's Riposte by 100% per stack.
Unyielding Shield - Throughout the encounter a Dutiful Attendant will spawn and channel this ability on the boss with the lowest health. Whilst the shield is active that boss will be immune to all damage. To remove the shield kill the Dutiful Attendant.
The below abilities will only be cast when other bosses have died.
Dredger Servant - This ability is cast when at least 1 boss has been killed and Castellan Niklaus is still alive. A group of Dredger Servants will appear in the encounter area and repeatedly cast 
Throw Food at random players. This deals a low amount of Nature damage to the players hit and is just an annoyance to the encounter. When they spawn kill them quickly as you don't want to have these alive during the intermission phase.
Castellan's Cadre - This ability is cast when Castellan Niklaus is the last boss alive. A new add is summoned into the encounter area when this is cast. The Veteran Stoneguard. This add will need to be tanked and casts 
Sintouched Blade which deals a large amount of Physical damage and increases their damage done by 50% per stack.
[Heroic] Castellan's Fury - This ability is cast when Castellan Niklaus is the last boss alive. When any add dies, everything within 12 yards of them will gain this buff which increases their damage dealt by 100% for 18 seconds. Ensure no adds are killed near Castellan Niklaus or the Veteran Stoneguard.
When any boss gets to 50% this phase is triggered.
Each player in the raid will have an assigned location in the room and the intermission will begin. If you do not reach this spot before the intermission begins you will die.
Please note, the intermission changed many times during Beta. The two latest versions are as follows: 1) Once the intermission starts you will see a spot on the ground near you illuminate, this spot will either be in front/behind/to your left/right. 2) The adds on the dance floor will move in the direction as dictated by the boss, it will always be one tile away. The below footage is from the most recent Mythic test.
If you reach your next spot correctly, you will gain a stack of 
Fancy Footwork, increasing your haste by 3% per stack for 30 seconds.
If you fail to reach your next spot, you will be hit by 
Wrong Moves and lose all stacks of Fancy Footwork.
There are two main changes to this fight for Mythic difficulty.
When a boss is killed they will reappear as an Afterimage to do 1 cast and then despawn throughout the remainder of the encounter, the abilities they cast are as follows:
Baroness Frieda - She will cast Dreadbolt Volley and this will need to be interrupted.
Lord Stavros - He will cast Dark Recital which will require you to pair up and move.
Castellan Niklaus - He will summon the Dutiful Attendant which will channel Unyielding Shield into the lowest health boss. This will need to be killed ASAP when it spawns.
Please note: None of these afterimages can spawn during an intermission phase.
There is also a raid mechanic which will require coordination called 
Dancing Fever.
This mechanic will apply 3 stacks of this debuff to 5 players in the raid, to remove a stack of the debuff the player must jump. When a stack of the debuff is removed it will deal raid wide damage. If the debuff expires on the player they will die.
Coordination is required to space out the damage by having set people jump, or powering through it with healing cooldowns to get it done quickly.
This section will be updated once a strategy has been devised for Mythic on live servers
On Mythic your Shadow Damage taken will be higher from the Dancing Fever Mechanic.
Castellan Niklaus + Baroness Frieda Swing Timer: 1.5s (Curse of Weakness 1.8s)
Lord Stavros Swing Timer: 1.3s (Curse of Weakness 1.5s)
If you kill Baronness Last, have Celestial Brew and/or Dampen Harm or Zen Meditation active for Soul Spikes.
Try to have Celestial Brew active for the 2nd stack of Evasive Lunge / Duelist's Riposte.
Remember to Touch of Death the bosses, you will get multiple uses of it during the encounter.
[Heroic] Tiger's Lust will clear stacks of Two Left Feet. Abilities such as Roll / Chi Torpedo will generate fewer stacks for a longer distance covered.
If you kill Baronness last, have Demon Spikes and/or Fiery Brand, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
If you kill Castellan Niklaus second or third utilise Sigil of Chains to bring Dredger Servants together for cleave DPS.
[Heroic] If you kill Lord Stavros last you can Infernal Strike to cover long distances and only gain one stack of Two Left Feet.
If you kill Baronness last, have Shield of the Righteous and/or Ardent Defender, Guardian of Ancient Kings, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
[Heroic] If you kill Lord Stavros last you can use Divine Shield or Blessing of Freedom to remove Two Left Feet.
You can reset the cooldown of your Taunt with Heroic Leap should you need multiple.
Evasive Lunge is blockable. Ensure Shield Block is active for each cast.
If you kill Baronness last, have Shield Block, Ignore Pain and/or Shield Wall, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
[Heroic] If you kill Lord Stavros last you can Heroic Leap to cover long distances and only gain one stack of Two Left Feet.
If you kill Baronness last, have Ironfur stacks and/or Barkskin, Survival Instincts, an External cooldown available for Soul Spikes.
Ensure you are on high health for the 2nd stack of Evasive Lunge / Duelist's Riposte.
If you kill Lord Stavros last use Stampeding Roar to help the raid get in position for Dancing Fools.
[Heroic] If you kill Castellan Niklaus last you can use Soothe to remove Castellan's Fury.
[Heroic] If you kill Lord Stavros last you can use change form to remove Two Left Feet.
You have multiple taunts with Death Grip and Dark Command.
If you kill Baronness Last, have Icebound Fortitude, Vampiric Blood or an External cooldown available for Soul Spikes.