Tasked with guarding Castle Nathria's entry hall, the blind monster Shriekwing locates her victims with horrifying cries that reverberate of the chamber's walls. The last sound heard by trespassers in the Grand Walk is the monster's cry as she descends upon her prey.
Swap on each cast of 
Exsanguinating Bite.
Ensure you are on high health and have Active Mitigation up for Exsanguinating Bite as you will be unhealable after.
Ensure you are out of Line of Sight from Shriekwing when she casts 
Earsplitting Shriek.
Avoid the Sonar discs from 
Echoing Screech (Phase 1 - Heroic + Mythic) and Echoing Sonar (Phase 2 - All difficulties).
Blessing of Protection or can be used to remove stacks of 
Exsanguinated.
When hiding from Earsplitting Shriek pre-place your 
Transcendence at the boss so you can instantly teleport back.
Ensure 
Celestial Brew is active for Exsanguinating Bite so that your health does not dip too low (you can also use this after you are hit and it will still work at full effectiveness).
Help heal the raid during Phase 2 with 
Vivify (as you can't hit the boss anyway).
Ensure 
Fiery Brand is active for Exsanguinating Bite so that your health does not dip too low.
Infernal Strike can be used for quick movement around the room and to hide from Earsplitting Shriek.
Blessing of Protection and 
Divine Shield can be used to remove stacks of Exsanguinated.
Ensure 
Shield of the Righteous and/or 
Ardent Defender is active for Exsanguinating Bite.
You can help your co-tank in Phase 1 with 
Blessing of Sacrifice before they are hit with Exsanguinating Bite.
Help heal the raid during Phase 2 with 
Flash of Light and 
Word of Glory.
Ensure 
Shield Block is active for Exsanguinating Bite.
You can help your co-tank in Phase 1 with 
Intervene when they are tanking the boss.
Heroic Leap and Intervene are both useful tools for hiding from Earsplitting Shriek.
Ensure 
Ironfur and/or 
Barkskin is active for Exsanguinating Bite.
Stempeding Roar can be useful to make the raid hide faster from Earsplitting Shriek.
You can help heal the raid during Phase 2.
You may find it necessary to cast 
Death Strike before Exsanguinating Bite for the 
Blood Shield.
Anti-Magic Zone is useful on this encounter and is likely to be assigned by your healers for periods where you are standing in 
Sanguine Ichor puddles.
This is a two phase encounter where it plays upon the boss being a bat, it's blind and uses sound to locate you. As with bat fantasy it wants to make you bleed. Throughout both phases of the encounter the boss will attempt to locate players locations with its echolocation and strike them directly. Personal responsibility is at the core of this fight.
Positioning: You will want to have the boss in a position that allows you to get out of his Line of Sight quickly. Illustrated below is an example of this where the boss is positioned near a pillar so that the tank + melee DPS can run behind it when they need to get out of Line of Sight.
Sanguine Ichor - These pools are left on the ground after Echolocation and failing to hide from Earsplitting Shriek.
The damage from these pools do not stack so you can stack these up with no issue.
Exsanguinating Bite - This is the main tank mechanic of the fight, and is cast very frequently. When cast the active tank will receive 10 stacks of Exsanguinated which reduces 10% reduced healing and 5% more physical damage per stack. The bleed will also deal ticking damage. You will lose 1 stack every 1.5 seconds. It is best to use mitigation and be near full health before Exsanguinating Bite is cast to ensure that the period in which you are unhealable isn't lethal.
You will be doing a tank swap after each cast of Exsanguinating Bite. Ensure this is quick as after the tank has been hit they will take 50% more damage and receive no healing!
This ability will be cast on the player with the highest threat rather than the person who is tanking the boss.
Echolocation - The boss senses and marks up to 3 non-tank players. These players will have 8 seconds to move away from others as when this debuff expires 
Descent will be cast which will deal a moderate amount of Physical damage to all players nearby, and spawn Sanguine Ichor. It is best to not cleave any other players with this.
Earsplitting Shriek - The boss will stand still and cast this spell, if you are in line of sight of her when this cast ends you will take a large amount of sonic damage. Any players hit will receive an 8 second debuff and drop a pool of Sanguine Ichor at their location. It is best to have a predefined location to gather to minimise the amount of space that is covered by Sanguine Ichor.
Wave of Blood - This is cast throughout the phase and will deal a small amount of damage on cast but leave a 12 second DoT on the entire raid.
Blind Swipe - The boss will target a player within melee range and cast this spell. It will deal damage to all players in front of the boss within 12 yards.
[Heroic] Echoing Screech - The boss will target a random non-tank player. Shriekwing will begin by shooting a Sonar disc at this player and then shoot 4 more sets from her sides, these will bounce off pillars and walls. If any player is hit with any of these they will be horrified for 2 seconds and trigger Descent.
When the boss reaches 100 energy the boss will teleport to the middle of the room and Phase 2 will begin.
During this phase the boss will be immune from damage and have a 12 yard 
Blood Shroud ring around her. The boss will be untankable and will patrol around the room randomly.
Blood Shroud - This is the key mechanic of the phase. If you are ever within the 12 yard ring. The boss will..to quote the dungeon journal MURDER YOU.
Positioning: Throughout this phase you will want to not be in Line of Sight of the boss. Illustrated below is an example of this where the boss is patrolling around the room and everyone is hiding out of Line of Sight.
Earsplitting Shriek - Same Earsplitting Shriek from Phase 1, keep sight of where the boss is patrolling and stay hidden behind a pillar.
Echoing Sonar - As the boss moves around the room balls of Sonar will be fired and bounce around the room. If you are hit by any you will trigger Descent.
After all the energy has been used Phase 1 will begin again.
Shadow damage can be higher based on amount of time spent in Sanguine Ichor.
Shadow damage will be higher for Mythic due to 
Bloodlight stacks.
Swing Timer: 1.8s (Curse of Weakness 2.1s)
Blessing of Protection or can be used to remove stacks of Exsanguinated.
When hiding from Earsplitting Shriek pre-place your Transcendence at the boss so you can instantly teleport back.
Ensure Celestial Brew is active for Exsanguinating Bite so that your health does not dip too low (you can also use this after you are hit and it will still work at full effectiveness).
Help heal the raid during Phase 2 with Vivify (as you can't hit the boss anyway).
Ensure Fiery Brand is active for Exsanguinating Bite so that your health does not dip too low.
Infernal Strike can be used for quick movement around the room and to hide from Earsplitting Shriek.
Blessing of Protection and Divine Shield can be used to remove stacks of Exsanguinated.
Ensure Shield of the Righteous and/or Ardent Defender is active for Exsanguinating Bite.
You can help your co-tank in Phase 1 with Blessing of Sacrifice before they are hit with Exsanguinating Bite.
Help heal the raid during Phase 2 with Flash of Light and Word of Glory.
Ensure Shield Block is active for Exsanguinating Bite (It's blockable!).
You can help your co-tank in Phase 1 with Intervene when they are tanking the boss.
Heroic Leap and Intervene are both useful tools for hiding from Earsplitting Shriek.
Ensure Ironfur and/or Barkskin is active for Exsanguinating Bite.
Stempeding Roar can be useful to make the raid hide faster from Earsplitting Shriek.
You can help heal the raid during Phase 2.
You may find it necessary to cast Death Strike before Exsanguinating Bite for the Blood Shield.
Anti-Magic Zone is useful on this encounter and is likely to be assigned by your healers for periods where you are standing in Sanguine Ichor puddles.
The main change on Mythic is that you are no longer able to see the Sonar discs. However a new mechanic has been added to let you see these....
The Blood Lantern!
If you are within 4 yards of the Lantern you will receive a stacking debuff called Bloodlight. This debuff lasts 8 seconds and stacks, it will deal a small amount of damage per stack but this adds up quickly.
When the Lantern has been picked up the radius of the Lantern increases from 4 yards to 14 yards.
If the Lantern is hit by Descent it will trigger 
Ravenous Horrors which will cause you to wipe, therefore if any players trigger Descent on the Lantern you need to move the Lantern ASAP.
The locations of the Lantern, the Ranged and Melee will be pre-assigned.
On the pull the raid will be positioned as below (Red Cross = Lantern)
The reason for this is so that when the boss casts Echoing Screech it will be baited towards the Ranged/Healer camp (Blue Square) and they will then move around the pillar. This will mean that the majority of the Sonar discs will be in areas of the room with low or no traffic from players. Melee/Tank players at this point should dip into the area of the Lantern to gain vision of the Sonar discs to ensure they are not hit.
Below is a video of it inside the encounter:
When the boss casts Earsplitting Shriek the raid will hide as they did in Heroic and the ranged will then move back to their initial position (Blue Square)
This process can be repeated on any pillar should you need to move the boss after the intermission is over.
You will want to have a pre-assigned player to carry the Lantern during the intermission to ensure that it is both nearby and that the raid has the debuff that allows them to see the Sonar discs during the intermission.
The only assignments that will need to be done mid-fight is during the intermission to potentially call out where to run to hide and where you will tank the boss after the intermission is over to allow the raid to position properly.
Your tanking approach on this boss does not change from previous difficulties of the encounter. You will still swap after each cast of Exsanguinating Bite.