With the Sepulcher of the First Ones vunerable, devourers flood in to feed their hunger. Among these beasts is the ravenous Skolex. As the great worm consumes vast amounts of ephemra, the sepulcher is thrown out of balance and threatens to collapse onto itself.
This is a single plase encounter where you are aiming to not be overwhelmed by 
Empemera Dust stacks and avoiding all of the mechanics. In order to reset your Empemera Dust stacks the ENTIRE RAID must stack together which will force the boss to cast 
Ravening Burrow and move to your location, if you are INSIDE this knockback your stacks will be removed.
The basic flow of the fight is:
Tank Combo> Retch > Tank Combo >Retch >Raid Stacks to Move Boss > Soak the boss hit (Repeat)
Empemera Dust - Stacking DoT by various mechanics. Can be reset with Ravening Burrow.
Dust Blast - The furthest 3 players (and all players within 10 yards of them) are hit with this on each hit of the Tank Combo.
Devouring Blood - Skolex will fire bolts on melee player locations. Failure to move will apply a DoT and reduce your Haste by 33%!
Retch - Targets a random ranged player and make them the centre of this cone. Move out of it when it spawns to pre-designated locations.
Ravening Burrow - When all players (including Melee DPS & Tanks) are stacked together Skolex will burrow underground and reemerge at this location. Getting hit by the boss reemerging removes all Empemera Dust stacks.
Wormhole Jaws - Stack on your co-tank unless there's a Tank Combo happening. If there is no other player within 10 yards the tank will be hit twice.
If you Dodge/Parry the attack, Wormhole Jaws will not be triggered.
At full energy a 3 part Combo will happen. The hits will either be 
Rend or 
Riftmaw. Swap on each hit of Riftmaw.
Rend - Big stacking Bleed.
This bleed can be removed with 
Blessing of Protection, 
Stoneform (Dwarf Racial), 
Fireblood (Dark Iron Dwarf Racial) and .
Riftmaw - Large Shadow damage hit and applies debuff to increase damage taken by Riftmaw for 500% for 6 seconds. Swap after each hit!
[Heroic/Mythic] Rend and Riftmaw will be applied to everyone in front of the boss.
Skolex Swing Timer: 2s (Curse of Weakness 2.4s)
You should ideally be the main tank for this fight as if you Dodge the initial hit from Skolex your co-tank will not be hit by Wormhole Jaws.
You will have 
Celestial Brew available for each Tank Combo.
If you are playing with the 
Fiery Soul legendary you will have 
Fiery Brand available for every Tank Combo.
Fiery Brand if used part way through the first cast of the Tank Combo will last for all three hits.
Use 
Infernal Strike to move to the raid stack point.
Divine Shield and Blessing of Protection will remove the stacking bleed from Rend.
Alternate using 
Ardent Defender, 
Guardian of Ancient Kings and your free 
Word of Glory charges for the Tank Combos.
Spell Reflection can be used to deflect a stack of Ephemera Dust, however it is best used to mitigate damage from Riftmaw.
Rallying Cry is best used to help the raid survive whilst stacked together and getting knocked back.
Rend and Wormhole Jaws can be blocked.
Stampeding Roar is useful to help the melee move to the raid stack spot.
Rune Tap and 
Anti-Magic Shell are best used to mitigate damage from Riftmaw.
Deaths Advance negates the knockback from Ravening Burrow.
Wraith Walk to move to the raid stack point.
This is a single plase encounter where you are aiming to not be overwhelmed by Empemera Dust stacks and avoiding all of the mechanics. In order to reset your Empemera Dust stacks the ENTIRE RAID must stack together which will force the boss to cast Ravening Burrow and move to your location, if you are INSIDE this knockback your stacks will be removed.
The basic flow of the fight is:
Tank Combo> Retch > Tank Combo >Retch >Raid Stacks to Move Boss > Soak the boss hit (Repeat)
Bloodlust/Time Warp/Heroism is best used on Pull.
You should have groups set up to be Dust Blast baiters. Each group will have 3 ranged in them (can include healers) and they should swap after each Retch.
You should also have a plan in place for your raid movement. On Normal & Heroic this is fairly basic as you can move in a triangle with 3 raid markers.
On the above plan the ranged would start on Triangle, after Retch 1 move to Square, after Retch 2 the ENTIRE RAID moves to Triangle.
This forces the boss to move to Triangle and the ranged will now start on Square and move to Diamond after Retch.
On the same plan above. Bait Team 1 would start behind Triangle, after Retch 1 Bait Team 2 would stand behind Square, after the raid stacks and the boss moves it now reverts back to Bait Team 1 behind Square.
Empemera Dust - This is the main mechanic of the fight. It's a simple stacking DoT that is applied by 
Dust Flial (Unavoidable stack on the entire raid), and Dust Blast (targets furthest 3 players during tank combo). These stacks can be reset by standing in Ravening Burrow.
Dust Blast - After every hit of the tank combo Skolex will send out Dust Blast bolts to the THREE FURTHEST PLAYERS. These players will gain 1 additional stack of Empemera Dust each hit. On Heroic this will also deal damage (and apply stacks of Empemera Dust to all players within 10 yards of the people hit). These three players should be behind the ranged stack point but also be mindful to not be "ahead" of the group as they can be targeted by Retch.
Devouring Blood - This mechanic only applies to Melee DPS & Melee Healers. Aproximately every 20 seconds, Skolex will fire bolts on top of player locations within 20 yards. Move out of these before they land. If you are hit you will take a moderate burst of Shadow damage and have an 18 second DoT applied. Whilst this DoT is on the player their Haste will be reduced by 33%!
Retch - This mechanic is a key mechanic for all Ranged DPS & Ranged Healers. Aproximately every 35 seconds, Skolex will target a random ranged player and make them the centre of a conal ability. All players inside of this should move together to safety. As a raid you should have predesignated stack locations and move between those two spots.
Ravening Burrow - This is a key mechanic for the ENTIRE RAID. When all players (including Melee DPS & Tanks) are stacked together Skolex will burrow underground and reemerge at this location. There will then be an animation on the ground indicating that the boss is going to come back up. If you are inside of this you will be knocked back away from the centre of this spot and all stacks of Empemera Dust will be removed. If you do not get hit, your stacks will not be removed and you will likely die from taking too much damage.
In addition to stacking with the raid for Ravening Burrow there are two tank specific mechanics Wormhole Jaws & the Tank Combo.
Wormhole Jaws - Skolex will attack the closest player to the tank within 10 yards when the tank has been hit. If there is no other player within 10 yards the tank will be hit twice.
If you Dodge/Parry the attack, Wormhole Jaws will not be triggered.
When Skolex reaches full energy the Tank Combo will be triggered. This is composed of three hits of either Rend or Riftmaw. Ideally you will swap on each hit of Riftmaw.
Rend - This will deal a large burst of Physical damage and apply a bleed that lasts for 24 seconds. To help make damage intake earier you should aim to have these Bleeds on one tank. If you get a triple Rend combo either have all three on one tank and remove it, or have two on Tank A and one on Tank B.
This bleed can be removed with Blessing of Protection, Stoneform (Dwarf Racial), Fireblood (Dark Iron Dwarf Racial) and .
Riftmaw - This will deal a large burst of Shadow damage and apply a debuff that increases the damage taken by Riftmaw for 500% for 6 seconds. The time in between the first and the third cast is long enough to allow this to drop. If you get a triple Riftmaw combo, you will want to have Tank A take the first and third hit and Tank B take the second.
[Heroic/Mythic] On these difficulties Rend and Riftmaw will be applied to everyone in front of the boss. The tanks should be seperated for the combo and ensure that they are not facing the boss towards the Ranged camps. The Melee should be mindful of tank locations.
Skolex Swing Timer: 2s (Curse of Weakness 2.4s)
You should ideally be the main tank for this fight as if you Dodge the initial hit from Skolex your co-tank will not be hit by Wormhole Jaws.
You will have Celestial Brew available for each Tank Combo.
If you are playing with the Fiery Soul legendary you will have Fiery Brand available for every Tank Combo.
Fiery Brand if used part way through the first cast of the Tank Combo will last for all three hits.
Use Infernal Strike to move to the raid stack point.
Divine Shield and Blessing of Protection will remove the stacking bleed from Rend.
Alternate using Ardent Defender, Guardian of Ancient Kings and your free Word of Glory charges for the Tank Combos.
Spell Reflection can be used to deflect a stack of Ephemera Dust, however it is best used to mitigate damage from Riftmaw.
Rallying Cry is best used to help the raid survive whilst stacked together and getting knocked back.
Rend and Wormhole Jaws can be blocked.
Stampeding Roar is useful to help the melee move to the raid stack spot.
Rune Tap and Anti-Magic Shell are best used to mitigate damage from Riftmaw.
Deaths Advance negates the knockback from Ravening Burrow.
Wraith Walk to move to the raid stack point.
The bigest change to this encounter for Mythic is that mechanics now leave behind Residue making that space unavailable to be used for the rest of the encounter so you will now need to move the boss around the room.
Below is a screenshot from an Enrage pull I had on Mythic to show how full the room is.
Additionally Rend from the Tank Combo now lasts 45 seconds. This means that if you still have the debuff active from a previous Tank Combo it will be refreshed and have stacks added to it.
As with Heroic you will want to pre-assign your Dust Blast baiters and what your movement plan is.
You will want your movement plan to be mindful of how much movement you are doing as this fight will be a DPS check. The more movement you do, the less raid DPS you have.
This section will be updated once the boss has been defeated on Live Servers.
The Strategy that I used on PTR to reach the Enrage was to move the boss around the edge of the room whilst also keeping the distance between the two ranged spots as small as possible.
Otherwise the fight played as it would for Heroic.