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.
Phase 1 (Boss Phase)
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.
Phase 2 (Hiding Phase)
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.
After all the energy has been used Phase 1 will begin again.
Tank Damage Profile
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)
Help heal the raid during Phase 2 with Vivify (as you can't hit the boss anyway).
Vengeance Demon Hunter
You can help your co-tank in Phase 1 with Intervene when they are tanking the boss.
You can help heal the raid during Phase 2.