For eons Halondrus traversed the caverns of the Sepulcher of the First Ones fulfilling its sacred purpose of reclaiming ephemera and returning it to the great cycle. With intruders now throwing this pattern into anarchy, the ancient keeper will do whatever it must to maintain order.
This is a three phase encounter with two intermissions. The intermissions trigger at 75% and 45%.
During Boss Phases the boss is rooted in the ground and the raid must avoid tank beams and prevent Ephemeral Motes from touching the boss
During intermissions the boss moves to a new area and triggers explosions at set locations which knock you back. Don't fall off the cliffs!
During the Final Boss Phase the boss will create more 
Emphemeral Fissure than every other phase which means more Motes that need to be kept away.
[Heroic/Mythic] An additional beam rotates around the boss which the raid needs to avoid. The beam has gaps in the first two boss phases but no gaps in the final boss phase meaning the raid needs to rotate around the boss with the beams.
Seismic Tremors - Lines will shoot from the boss to the edge of the room and create an Emphemeral Fissure which spawns Ephemeral Motes.
Ephemeral Eruption - The motes cannot reach the boss, if they do you will wipe!
If you run into a mote it will do a small burst of damage to the player and all players within 6 yards and knock the orb away from the boss.
Eternity Engine - Passive damage. Whilst active motes are dragged into the boss. Every 20 seconds this increases in power, both in terms of damage dealt and the speed that motes are being dragged in.
Lightshatter Beam - Tank swap on each beam cast.
[Heroic] Spot the white lines, this indicates ones you need to put the tank beam on to break the shields on the Emphemera Motes.
Reclaim - The boss will apply a 3% absorb shield on it. Whilst the shield holds the raid and all motes will be dragged in. Keep the motes knocked away and break the shield.
Earthbreaker Missiles - Every player has this debuff applied to them and after the cast finishes they trigger a burst of Cosmic damage to themselves and all players within 6 yards. After a few seconds 
Aftershock will trigger from the pools on the ground.
Crushing Prism - Get dispelled in front of a pool. The areas left behind will slow Motes.
[Heroic] 
Planetcracker Beam - A rotating beam around the boss which deals a large amount of Cosmic damage every 0.3 seconds a player is in them. Avoid!
Relocation Form - This indicates the end of the Boss Phase (75% & 45%). A moderate burst of Physical damage is dealt each time a leg is pulled from the ground.
Make sure you exit the room after the boss leaves. The door will close after the boss goes through and you are left behind you die!
Earthbreaker Missiles & Crushing Prism are still used.
Shatter - Knocks the raid away from the location of the orb. Be careful to not get knocked off the cliffs!
Crushing Prism - Get dispelled to a side.
Boss spams 
Lance on the tank.
Reclamation Form - At the end of the intermission, the boss roots in the ground again dealing raid damage.
Reclaim is no longer cast.
Eternity Overdrive replaces Eternity Engine. Orbs are dragged in even faster and the passive raid damage is even higher!
[Heroic] Planetcracker Beam has no gaps!
Tanking During Intermission
Not Tanking During Intermission
Lance Cast Timer: 1.5s (Cannot be slowed, however is often delayed by spells).
Transcendence can be useful to get back in position after the Shatter knockback or to get around the Planetcracker Beam.
Zen Meditation can be used to mitigate damage from Lightshatter Beam.
Use 
Infernal Strike to get back in position after the Shatter knockback.
Blessing of Freedom can be used to remove slows on players with Crushing Prism.
During intermissions ideally your co-tank should have the boss as a lot of Paladin mitigation is based on your current position so you will be weaker than any other tank spec from this heavy movement phase.
Divine Shield and 
Blessing of Spellwarding can be used to run through the Planetcracker Beam to soak orbs in the Final Boss Burn.
Blessing of Protection can prevent the knockback from Shatter.
Lance can be blocked.
Use 
Charge to get back in position after the Shatter knockback.
Rallying Cry is best used for Earthbreaker Missiles during the Intermissions to help keep the raid healthy.
Use 
Skull Bash to get back in position after the Shatter knockback.
Stampeding Roar is useful help the raid spread for Earthbreaker Missiles during the intermissions.
Anti-Magic Shell will make you immune to the Planetcracker Beam allowing you to run through safely.
Death's Advance will negate the knockback from Shatter.
This is a three phase encounter with two intermissions. The intermissions trigger at 75% and 45%.
During Boss Phases the boss is rooted in the ground and the raid must avoid tank beams and prevent Ephemeral Motes from touching the boss
During intermissions the boss moves to a new area and triggers explosions at set locations which knock you back. Don't fall off the cliffs!
During the Final Boss Phase the boss will create more Emphemeral Fissure than every other phase which means more Motes that need to be kept away.
[Heroic/Mythic] An additional beam rotates around the boss which the raid needs to avoid. The beam has gaps in the first two boss phases but no gaps in the final boss phase meaning the raid needs to rotate around the boss with the beams.
Bloodlust/Time Warp/Heroism is best used in Phase 3 for the final boss phase.
Your tanks should manage who is tanking during the intermission. I would recommend that one tank has the boss to make healing more reliable. Ideally this tank should NOT be a Protection Paladin as they will not have their mitigation active due to movement.
For Heroic you should have pre-assigned locations for the raid in Phase 3 as the Planetcracker Beam will divide the room in two and you need a somewhat even split to manage all of the Motes.
Seismic Tremors - Lines will shoot from the boss to the edge of the room and create an Emphemeral Fissure which spawns Ephemeral Motes.
Ephemeral Eruption - The motes cannot reach the boss, if they do you will wipe!
If you run into a mote it will do a small burst of damage to the player and all players within 6 yards and knock the orb away from the boss.
It's very important to remind players of the splash damage component as multiple players being hit adds up and in Phae 3 can become unhealable. Have trust that if a player is in the path of a Mote, they will knock it back.
The simplest way of handling this is to just plant yourself in front of a Mote and let it fly into your back. Purposely running into them will be a throughput loss and should only be reserved for emergency situations.
Eternity Engine - Passive damage. Whilst active motes are dragged into the boss. Every 20 seconds this increases in power, both in terms of damage dealt and the speed that motes are being dragged in.
Lightshatter Beam - Tank swap on each beam cast.
Tanks should taunt swap during the cast as it will re-cast often and taking two of these in a row will require many cooldowns to survive.
[Heroic] Spot the white lines, this indicates ones you need to put the tank beam on to break the shields on the Emphemera Motes.
Reclaim - The boss will apply a 3% absorb shield on it. Whilst the shield holds the raid and all motes will be dragged in. Keep the motes knocked away and break the shield.
Focus on breaking the shield here, whilst it may be tempting to keep motes away as long as they don't go into the boss that's all that matters.
Earthbreaker Missiles - Every player has this debuff applied to them and after the cast finishes they trigger a burst of Cosmic damage to themselves and all players within 6 yards. After a few seconds Aftershock will trigger from the pools on the ground.
Crushing Prism - Players with this debuff will be slowed and take ticking damage. Once they are in front of an Emphemeral Fissure they should call for a dispell as the areas left behind will slow Motes.
[Heroic] Planetcracker Beam - This new mechanic on heroic attempts to keep you from standing still. A beam will be rotating around the boss and the active parts of the beam will change periodically. If you are hit by these you will take a large amount of Cosmic damage every 0.3 seconds.
In Phase 1 only one of these areas will be active, and in Phase 2 three will be active.
Relocation Form - This indicates the end of the Boss Phase (75% & 45%). A moderate burst of Physical damage is dealt each time a leg is pulled from the ground.
Make sure you exit the room after the boss leaves. The door will close after the boss goes through and you are left behind you die!
Earthbreaker Missiles & Crushing Prism are still used.
Shatter - The boss will activate an orb which will knock the raid away. If you are inside of the area of this orb you will take a lethal amount of damage. If you are outside of the area you will take a burst of damage and be knocked away. Be careful to not get knocked off the cliffs!
Crushing Prism - Similar to the spell in Phase 1 & 2 this will slow players and deal damage over time. Players should move to the side of the room and call for a dispell.
During this phase the boss will spam cast Lance on the tank. This tank will be taking a very large amount of damage and require some healer attention.
Reclamation Form - At the end of the intermission, the boss roots in the ground again dealing raid damage.
Reclaim is no longer cast.
Eternity Overdrive replaces Eternity Engine. Orbs are dragged in even faster and the passive raid damage is even higher!
[Heroic] Planetcracker Beam has no gaps!
Tanking During Intermission
Not Tanking During Intermission
Lance Cast Timer: 1.5s (Cannot be slowed, however is often delayed by spells).
Transcendence can be useful to get back in position after the Shatter knockback or to get around the Planetcracker Beam.
Zen Meditation can be used to mitigate damage from Lightshatter Beam.
Use Infernal Strike to get back in position after the Shatter knockback.
Blessing of Freedom can be used to remove slows on players with Crushing Prism.
During intermissions ideally your co-tank should have the boss as a lot of Paladin mitigation is based on your current position so you will be weaker than any other tank spec from this heavy movement phase.
Divine Shield and Blessing of Spellwarding can be used to run through the Planetcracker Beam to soak orbs in the Final Boss Burn.
Blessing of Protection can prevent the knockback from Shatter.
Lance can be blocked.
Use Charge to get back in position after the Shatter knockback.
Rallying Cry is best used for Earthbreaker Missiles during the Intermissions to help keep the raid healthy.
Use Skull Bash to get back in position after the Shatter knockback.
Stampeding Roar is useful help the raid spread for Earthbreaker Missiles during the intermissions.
Anti-Magic Shell will make you immune to the Planetcracker Beam allowing you to run through safely.
Death's Advance will negate the knockback from Shatter.
This fight was changed multiple times on PTR after testing had finished and Mythic has been redesigned completely. This page will be purely speculative of my understanding of the dungeon journal and be updated once guilds have pulled it on Live.
The main change in this fight is the addition of a new mechanic 
Volatile Charges. This charge will detonate and wipe the raid on the following conditions:
- It has been idle for 10 seconds.
- It has been hit by a Mote or Lightshatter Beam.
After handling the charge the player will be debuffed with 
Charge Exposure for 16 seconds.
Volatile Charges will need a rotation of players to handle it as it can not be in one players hands for more than 10 seconds.
I currently speculate that one of these will be active per phase (1 in Phase 1, 2 in Phase 2 and 3 in the Final Boss Burn).
This will require a rotation of two players to handle it
| Floor 5s | Player 1 5s | Player 1 Drop | Floor 5s | Player 2 5s | Player 2 Drop |
| 16s (Player 1 debuff) | 11s (Player 1 debuff) | 6s (Player 1 debuff) | 1s (Player 1 debuff) |
This section will be updated once the boss has been defeated on Live Servers.
I do not speculate that the fight will change all too much other than players handling the Volatile Charges will need to be hyper aware of avoiding mechanics that can blow it up and wipe the raid.