The devourers consume anima wherever they can find it. With drought afflicting the Shadowlands, it is no surprise that the hungriest and most dangerous of the devourers is drawn to the abundant store of anima here in the depths of Castle Nathria.
The boss will leech health from the tank after each auto attack. After each attack it will gain a stack of 
Growing Hunger which increases the leech. Swap frequently to keep this low.
Have mitigation and/or a cooldown active for 
Overwhelm.
Whilst not tanking you can help soak 
Gluttonous Miasma or 
Obliterating Rift.
When the boss reaches 100 energy, move him to the side of the room to give the raid more space to move from 
Consume.
Purifying Brew after each Overwhelm for large amounts of 
Stagger removal + Purified Chi stacks.
Pre-place 
Transcendence at the ranged clump of players before pulling so you can Transcendence out for each Consume.
Celestial Brew is useful to have active during 
Expunge as healers will be busy moving and keeping the raid healthy.
Ensure 
Demon Spikes is active for Overwhelm.
After you drag the boss to the side for Consume, 
Infernal Strike back to the raid.
Ensure you have 
Shield of the Righteous and/or 
Ardent Defender active for Overwhelm.
Word of Glory after each Overwhelm for large amounts of healing.
During periods of tanking downtime you can heal your co-tank with Word of Glory.
Ensure 
Shield Block is active for Overwhelm.
Spell Reflection can be used to deflect Expunge.
After you drag the boss to the side for Consume, 
Heroic Leap back to the raid.
Rallying Cry will likely be assigned for Consume.
Ensure you have 
Ironfur stacks and/or 
Barkskin / 
Survival Instincts active for Overwhelm.
Whilst not tanking you can be in another form to do more DPS.
Stampeding Roar should be used to help the raid run out for Consume.
Death Strike after each Overwhelm for large amounts of healing.
Death's Advance will negate the pull from Consume.
Anti-Magic Zone will likely be used during Consume to help mitigate the raid damage.
This is a single phase encounter with a single boss. There are a lot of positional requirements where the raid will need to flex and adapt to the mechanics as they come.
Growing Hunger - This is the primary tank mechanic of the fight. Every melee hit the boss will leech health and gain a stack of Growing Hunger which increases the power of the leech effect by 8% per stack. The stack resets when the boss hits a new target.
Overwhelm - Large Physical damage hit on a set timer. Ensure you have mitigation active and/or a cooldown for this.
Gluttonous Miasma - This debuff will be applied to several non-tank players every 24 seconds. The debuff is 24 seconds duration so will always be present during the encounter. Players with the debuff will be immune to healing, take a small amount of ticking damage (as well as the raid wide damage) and leech health from all players within 5 yards of them. A buddy system is required to counter this mechanic to ensure that these players do not die, you will want at least 2 other players to feed their health into the debuffed raid member.
Desolate - Raid wide unavoidable moderate Shadow damage every ~20 seconds.
Volatile Ejection - 3 players will be marked and a line will be shot at each of them. Anyone in that line will take a moderate amount of Shadow damage and receive a debuff increasing their damage taken by Volatile Ejection by 500% for 35 seconds. However, this ability is cast every ~30 seconds so if you get hit by one accidentally and are then marked with one you will likely die. It is important to note that the width of the lines are wide so you will need to be careful in melee.
Expunge - All players will have an Expunge circle around them and after 5 seconds a moderate amount of Shadow damage will be dealt to all players within the circle. The size of the circle is based on the players missing health.
[Heroic] Obliterating Rift - Whenever an Expunge debuff expires an Obliterating Rift orb will now spawn at that location. These orbs are permanent and can be removed from the encounter space by running into them, however this will deal a large amount of Shadow damage. Players with immunities can soak these, however they can also be ignored as long as there is space to run away from the boss for Consume.
Consume - When the boss is on full energy Consume will be cast. This is an 8 second long cast where health will be leeched from the raid to the boss. The closer you are to the boss, the more health is leeched. You should aim to move the boss to an edge of the room prior to this ability to allow the raid to get a larger distance from the boss to minimise the leech.
There are two main changes for Mythic.
Essence Sap - Each tick of Gluttonous Miasma will now apply a stacking debuff increasing damage taken by 10% per stack. This debuff lasts 20 seconds, so you will be able to soak every other set of Gluttonous Miasma.
Volatile Ejection - This now targets 4 players (up from 3).
This section will be updated once a strategy has been devised for Mythic on live servers
Swing Timer: 1.8s (Curse of Weakness 2.1s)
Purifying Brew after each Overwhelm for large amounts of Stagger removal + Purified Chi stacks.
Pre-place Transcendence at the ranged clump of players before pulling so you can Transcendence out for each Consume.
Celestial Brew is useful to have active during Expunge as healers will be busy moving and keeping the raid healthy.
Ensure Demon Spikes is active for Overwhelm.
After you drag the boss to the side for Consume, Infernal Strike back to the raid.
Ensure you have Shield of the Righteous and/or Ardent Defender active for Overwhelm.
Word of Glory after each Overwhelm for large amounts of healing.
During periods of tanking downtime you can heal your co-tank with Word of Glory.
Ensure Shield Block is active for Overwhelm.
Spell Reflection can be used to deflect Expunge.
After you drag the boss to the side for Consume, Heroic Leap back to the raid.
Rallying Cry will likely be assigned for Consume.
Ensure you have Ironfur stacks and/or Barkskin / Survival Instincts active for Overwhelm.
Whilst not tanking you can be in another form to do more DPS.
Stampeding Roar should be used to help the raid run out for Consume.
Death Strike after each Overwhelm for large amounts of healing.
Death's Advance will negate the pull from Consume.
Anti-Magic Zone will likely be used during Consume to help mitigate the raid damage.