As the ancient aqir arose from the desert sands, their prophets set about the construction of an obsidian destroyer imbued with the essence of the Old Gods. Driven by an insatiable thirst for magic, Maut consumed the mana of its creators once it awoke and left their corpses to rot under the scorching sun of Uldum.
This fight is a two phase encounter where in Phase one you are able to damage the boss and your goal is to prevent/control the mana gain of the boss. Once the boss reaches full mana they will gain an absorb shield and start a 1 minute long cast, if this cast is successful you will wipe, burn through the mana shield and get back to Phase 1 to damage the boss again.
Shadow Claws - This is the stacking tank mechanic of this encounter, it will deal Physical damage and apply Shadow Wounds which deals shadow damage over time and stacks.
Consuming Shadows - The raid will take increasing amounts of Shadow damage during this phase which scales from the amount of Mana Maut has. Towards the end of Phase 1 this will be high and the healers will be spending more of their attention towards the raid as a result (less tank attention).
Devour Magic - Throughout Phase 1 several non-tank players will have this debuff cast on them, they will have a large ring around them and when the debuff expires they will spawn a 
Devoured Abyss zone. These zones silence, drain Mana, prevent healing, inflict shadow damage and grant immunity from magic effects everything in them.
Dark Manifestation - This is the other main tank mechanic of the fight. This will create a void zone on the floor in the room which will suck nearby players in, it will then explode and spawn an add with the same name.
The add spawns with 1 HP, but has a large Mana pool which acts as a shield due to 
Dark Aegis.
These adds will constantly attempt to cast 
Dark Offering which will give Maut 20% of their Mana, as your goal in this phase is to not let the boss gain Mana (until you want to), you do not want the add to cast this therefore you will need to drag them into the Devoured Abyss zones. These zones will silence the adds and drain their Mana.
Please note: Whilst the adds are in the Devoured Abyss zones they will only take Physical damage as they are immune to all magic.
When one of these adds are close to the Maut, he will consume them and take all of their remaining Mana. Therefore you can use this to control when you Phase.
Stygian Annihilation - Maut will cast this spell fairly infrequently during Phase 1 and it will deal a lethal amount of damage to all players in the raid. However, if you are stood within a Devoured Abyss zone you will not take any damage from this but you will be silenced for the duration.
[Heroic] 
Black Wings - The boss will target a Melee DPS* player (this also includes any player in Melee range of the boss, so Ranged DPS and Healers need to ensure they are away from the boss or on the Melee clump) and start to cast this ability on them, anybody caught within a 40 yard cone from the boss will take Physical damage and be knocked back.
*Please note: Maut always cast this in a direction of a Melee DPS player which is why on the Map at the top of the page I have suggested to have them in their own distinct location away from everyone else.
Once Maut has reached 100% Mana he will run to the middle of the room and transition into Phase 2.
Once Maut has started this Phase he will cast 
Obsidian Skin which will make him inactive, take no damage from his health and have a Mana shield instead.
This cast is 1 minute long and if it completes, you will wipe. Also, any damage dealt to Maut will be reflected back to the attacker so the raid should be stacked for efficient healing.
Forbidden Ritual - During the entirety of this Phase Maut will attempt to regain his Mana, there will be orbs of Mana floating to the boss from the edges of the room, if they reach Maut he will regain all of his Mana.
If a player intercepts the orb they will gain the Forbidden Mana buff.
When contact has been made with the orb the raid will take Arcane damage based on the distance it has travelled. If it is soaked near the spawn the damage will be low, if it's near the boss the damage will be high.
Forbidden Mana - Once collected this will place an aura around the player which will increase Mana Regeneration by 150% and Healing Done by 50% for all players within 20 yards for 8 seconds. It is imperative that this is soaked so that you can push the high amounts of healing required in this phase, and also allows for healers to regenerate their Mana.
[Heroic] 
Drain Essence - This debuff is applied to several players throughout this Phase and for each second they are on a player, Maut will gain 1% Mana back. This debuff can be dispelled but will deal Shadow damage and drain Mana from all players within 10 yards.
Ideally you want the players with this debuff to move out ASAP, but you can also elect to dispel it in the raid as you will be regaining Mana from Forbidden Mana.
There is one new mechanic for this fight on Mythic.
Ancient Curse - This debuff will be applied to everybody in the raid and if it has not been removed after 24 seconds, that player will die.
This debuff can be removed by having a Mage, Druid, Shaman remove the curse from you, or by running into a Devoured Abyss zone.
Each time a Curse is removed it will deal a small amount of Physical damage to the whole raid so you will want to stagger these out.
We found it best to have Healers + Tanks get dispelled and for other players to take turns removing their debuff in the Devoured Abyss zones. (Example: Melee remove at 15s remaining on debuff, Group 2 ranged at 10s remaining, Group 3 ranged at 5s remaining)
2 Tanking this fight on Mythic is relatively simple where you will have the add tank take the first stack of Shadow Wounds from the boss and then pick up the first add.
When the first add is on ~65% mana the boss tank can bring it into the boss, which will give you enough time to handle the second round of Ancient Curse and then bring the second add into the boss before the third add spawns to enter Phase 2.
The boss tank will have ~4/5 stacks of Shadow Wounds so they will need to stay in the raid healing until their debuff has expired and whomever your raid has assigned to pick up the Forbidden Mana orbs will need to be quick and watch out for the visual from the pillars to indicate where they are spawning from.
Boss Tank:
Physical 10% Shadowlaws & 10% Ancient Curse on Mythic
Shadow 25% Shadow Wounds
Add Tank:
There are benefits with both strategies and ultimately it is up to your raid leader to decide which you go for.
3 Tanking:
The purpose of the third tank is to completely manage the adds in Phase one, and to help with Forbidden Mana orbs in Phase two.
The third tank will keep all of the adds in a single spot, and if they spawn too far away from them the tank that is not tanking the boss can bring it over to that tank (without going through the boss), the other two tanks will swap on ~2-3 stacks of Shadow Wounds.
2 Tanking (With Multi-Taunt):
If you play with a tank that has multi-taunt options (Monk, Death Knight, Warrior) you can still have one tank manage the adds and the other tank the boss with a 2 tank strategy, where you have the tank who can AoE taunt on the boss to start with, once two adds have spawned on the next cast of Stygian Annihilation you can do a taunt swap and carry on from there. This will mean that you will roll through your defensive cooldowns as you will have one prolonged tanking window rather than multiple short ones.
2 Tanking (One boss tank, one add tank):
Finally there is an option to have a single tank keep the boss for the entire phase and use all of their cooldowns to survive and rotate who tanks the boss each Phase 1 (if necessary).
You will have the add tank take the first stack of Shadow Wounds from the boss and then pick up the first add.
The boss tank will have ~4/5 stacks of Shadow Wounds so they will need to stay in the raid healing until their debuff has expired.
Black Ox Statue can be useful here to ensure the adds do not move towards the boss
You can taunt multiple adds at the same time by placing Black Ox Statue near them and casting 
Provoke on the Statue
Your high mobility is very useful to soak the orbs in Phase 2 quickly to lower raid damage
Transcendence is very useful for the very first Forbidden Mana orb in Phase 2 as you can get into the raid very quickly to buff them.
Infernal Strike can be utilised to soak the orbs in Phase 2 quickly to lower raid damage
Blessing of Spellwarding and 
Blessing of Sacrifice can be used on high burst DPS classes during Phase 2 to help keep them alive from the reflected damage
Rallying Cry is a strong raid cooldown to use to help keep the raid alive at the end of Phase 1 or during Phase 2 where damage intake is very high
You can taunt two adds at once should you need to conduct a tank swap with 
Taunt and 
Heroic Leap to reset the cooldown of Taunt
Heroic Leap can be utilised to soak the orbs in Phase 2 quickly to lower raid damage
[Mythic] You can remove Ancient Curse with 
Remove Corruption
You can taunt two adds at once should you need to conduct a tank swap with 
Death Grip and 
Dark Command
If 
Anti-Magic Shell is active when Maut casts Shadow Claws you will not gain a stack of Shadow Wounds