The nefarious Kel’Thuzad awaits at the apex of the soul river, allowing the lich to draw upon an unlimited well of power. All his countless schemes and machinations have led to this final confrontation, where he has plotted the mortal champion’s ultimate demise in service of his true master.
The tank mechanic of this fight is 
Soul Fracture. This increases the damage taken from the tank by 500%. Fragments of the tank will also appear around the room. These fragments are the top DPS priority and need to have their 
Piercing Wail casts interrupted.
Oblivion's Echo circles will be placed on several players, silencing everyone within them. After they are placed on the ground a Frostbound Devoted add will spawn. These adds fixate on a random player and attempt to explode on them.
Glacial Spikes will spawn from 
Glacial Wrath. They passively lose 5% Health per second and when they die, they explode leaving a stack of 
Frozen Destruction on the raid.
When Kel'Thuzad is Out-Of-Mana in Phase 1, he will cast 
Howling Blizzard and you need not be in the Frost Patches as they will explode after 20 seconds.
Soak 
Frost Blast with the raid to split the damage.
If you are inside in the intermission focus on avoiding the 
Shadow Fissures and 
Freezing Blasts.
If you are outside in the intermission focus on interrupting 
Banshee's Cry from the Soul Reavers, and dodge the 
Demolish from the Unstoppable Abominations.
In the final phase, move out of the Deep Freeze patches.
Frostbound Devoted can be stunned with 
Leg Sweep and they will begin their Fixate cast again when the stun is over allowing you to keep a group of them stationary for a long time with a single stun. 
Ring of Peace can also be useful here to knock a loose add towards the rest so they die in the same spot.
Tiger's Lust can be used to remove the root from Frost Blast.
Transcendence can be useful to reposition after collecting your souls from the tank mechanic.
The only really good opportunity to use 
Zen Meditation during this encounter is during the 2nd or 3rd round of Glacial Spikes blowing up.
Sigil of Chains can be useful to grip Frostbound Devoted add together.
Sigil of Misery can be used to stop the Fixate from Frostbound Devoted adds, when the fear ends they will begin their Fixate cast again allowing you to keep them stationary for a prolonged period of time.
Sigil of Silence DOES NOT work to interrupt the Banshees.
Blessing of Freedom can be used to remove the root from Frost Blast.
Blessing of Spellwarding can be placed on a player to allow them to solo soak Frost Blast.
If you are a Kyrian Paladin 
Divine Toll will interrupt Banshees allowing you to interrupt multiple at once.
Frostbound Devoted can be stunned with 
Shockwave and they will begin their Fixate cast again when the stun is over allowing you to keep a group of them stationary for a long time with a single stun.
Ice Shard is blockable.
Spell Reflection is best used when the Glacial Spikes are blowing up to mitigate damage taken.
Rallying Cry is best used to help the raid whilst the Glacial Spikes are blowing up.
Shapeshifting will remove the root from Frost Blast.
Stampeding Roar is useful to get players together for Glacial Spikes.
Anti-Magic Shell can be used to avoid the root from soaking Frost Blast & 
Wraith Walk will remove it.
Anti-Magic Shell can be used to immune stack(s) from the Glacial Spikes blowing up.
Anti-Magic Zone is best used to mitigate raid damage taken from the Glacial Spikes blowing up.
Gorefriend's Grasp can be useful to grip Frostbound Devoted adds together.
If you are a Necrolord Death Knight be careful when using 
Abomination Limb whilst Frostbound Devoted are active as you could grip the one fixated on you to you and blow up the raid.
This is a three-phase encounter where you will force Kel'Thuzad to enter his Phylactery to destroy his Remnant and finally defeat him. You can send teams of players inside the Phylactery to fight against the Remnant of Kel'Thuzad. However, you will need enough players outside to fight against the adds that will spawn during this.
Dark Evocation - Any dead players or Frostbound Devoted will be revived each time this is cast. (players will be resurrected and mind-controlled)
As the fight goes on, you will be fighting against more and more Frostbound Devoted adds (and hopefully not more mind-controlled players).
Ice Shard - This is a replacement for a melee swing. The boss can still melee swing just has Ice Shard as an alternative.
Soul Fracture - Be very mindful of this cast as once it begins, a tank swap is required immediately. When the cast completes, the targeted tank will receive 3 stacks of 
Soul Exhaustion, increasing damage taken by 500%. In addition to this, 3 copies of themselves will be created around the edge of the room.
These will be casting Piercing Wail, dealing a high amount of Shadow damage to the raid. This can be interrupted by players or silenced by placing Oblivion's Echo on them.
Once they are defeated, the tank can collect their Soul and remove 1 stack of Soul Exhaustion.
You can taunt during the cast as the target is fixed once the cast begins.
Oblivion's Echo - Multiple players, will receive this debuff throughout this phase. Any players (or tank souls) within 10 yards will be silenced, and after 6 seconds, a field of silence will be dropped at their location. After a further 6 seconds, a Frostbound Devoted add will spawn from each silence field.
Each subsequent Phase 1 will increase the number of players targeted by Oblivion's Echo. During our testing, this started with 2 players being targeted.
Frostbound Devoted
These adds will fixate on a random player and cast 
Relentless Haunt.
If they reach their fixated player, they will explode, dealing a large amount of Shadow damage to people nearby.
You can stun/CC these adds. However, it will make them re-fixate, so be ready to move if it's on you!
Glacial Wrath - Multiple players will receive this debuff throughout this phase. After 5 seconds, a Glacial Spike will spawn at their location.
The Glacial Spikes will lose 5% Health every second passively, and when they reach 0 Health, they will trigger Frozen Destruction. The damage from Frozen Destruction stacks, so you want to make sure the deaths of the Glacial Spikes are controlled.
Each subsequent Phase 1 will increase the number of players targeted by Glacial Wrath. During our testing, this started with 2 players being targeted.
Frost Blast - This meteor style effect will be placed on one player, and the damage from Frost Blast splits with any players in the radius. In addition to this, any players hit by Frost Blast will be rooted in 
Frozen Binds for 12 seconds. The root can be removed with a wide array of tools but can be problematic if you have a Frostbound Devoted fixated on you.
The Frost Blast can be solo soaked with an immunity.
Howling Blizzard - When Kel'Thuzad is out of mana, this spell will be cast, slowly filling the room with Ice. If you are stood in any Ice patches after 20 seconds, you will take a lethal amount of Frost damage.
Adds will spawn in the outside phase, which needs to be handled properly.
Unstoppable Abomination
Two of these will spawn in the intermission. Each tank should take one each and face them towards a wall.
Demolish - This 3-second cast will shoot a wave of Shadow damage in front of them in a straight line. You can move out of the way of this by sidestepping.
Soul Reaver
Three of these will spawn in the intermission. These should not be tanked as their melee swings are very high. DPS players should be mindful of their threat as they will likely die if one gets too close to them.
Banshee's Cry - This cast should be interrupted as often as possible. It will deal a large amount of damage to random players.
[Heroic] Banshee's Cry - Each successful cast increases the damage of the spell by 25%.
[Heroic] Undying - You do not want to kill these adds ASAP as any adds that die will revive after 10 seconds and gain the Undying buff, which will make them immune to CC.
[Heroic] 
Necrotic Empowerment - If any adds are alive when Kel'Thuzad is revived, they will be buffed with Necrotic Empowerment. This will increase their damage by 25% and make them immune to all forms of Crowd Control.
Vengeful Destruction - When players enter the Phylactery, the Kel'Thuzad will begin to cast this spell. If, after 45 seconds, they have not removed 33% of the Remnant of Kel'Thuzads health, this cast will complete, dealing a very large amount of Shadow damage players outside. If they do remove 33% of his health, the cast will be interrupted.
Kel'Thuzad will be revived by the Phylactery and gain one stack of 
Necrotic Surge when this phase ends. Each stack increases his damage by 5% and the number of targets for Glacial Wrath and Oblivion's Echo.
A team of players can enter the Phylactery and fight against the Remnant of Kel'Thuzad. Each time you enter, you can reduce his health by a maximum of 33% each time (it will take 3 rounds of Phase 2 to kill him).
To enter the Phylactery, you will need to run on top of Kel'Thuzad and use the extra action button.
Sinister Miasma - Stacking DoT to all players inside the Phylactery.
Shadow Fissure - This is constantly cast at players' locations, and if these hit any players, they will be knocked back and take a large amount of Shadow damage.
Freezing Blast - The Remnant of Kel'Thuzad will point towards a player and shoot a line of Ice. Any players hit will be rooted for 4 seconds and take a large amount of Frost damage.
[Heroic] 
Glacial Winds - When the Remnant of Kel'Thuzad is at 33% health (the final Phase 2), Tornadoes will spawn at his location and spin towards the edge of the room. Any players hit will be rooted for 4 seconds.
The recommendation for the intermission is to send melee DPS & mobile ranged DPS to be stacked together and move around the Remnant.
Undying Wrath - After 45 seconds, the Remnant of Kel'Thuzad cast this spell. This will deal a very large amount of Shadow damage to every player inside and push them out of the Phylactery, resulting in a wipe.
Soul Marked - Whilst you are inside the Phylactery, you cannot re-enter until the Remnant has been defeated.
Note: This debuff will reset once you return to Phase 1.
This final phase of the encounter will incorporate mechanics from Phase 1 and 2 and a new mechanic.
Ice Shard - Basic tank hit.
Frost Blast - Frost Meteor.
Sinister Miasma - Stacking DoT.
The Unstoppable Abiminations and Soul Reavers from the Intermissions will spawn during this phase in addition to the Frostbound Devoted.
Deep Freeze - Patches of Ice will slowly fill the encounter area. Standing in these Ice patches will deal a high amount of Frost damage every second.
This adds a DPS check to the phase; therefore, it would be advisable to use Bloodlust/Heroism/Time Warp here.
Kel'Thuzad Swing Timer: 1.5s (Curse of Weakness 1.8s)
Unstoppable Abomination Swing Timer: 1.5s (Curse of Weakness 1.8s)
Frostbound Devoted can be stunned with Leg Sweep and they will begin their Fixate cast again when the stun is over allowing you to keep a group of them stationary for a long time with a single stun. Ring of Peace can also be useful here to knock a loose add towards the rest so they die in the same spot.
Tiger's Lust can be used to remove the root from Frost Blast.
Transcendence can be useful to reposition after collecting your souls from the tank mechanic.
The only really good opportunity to use Zen Meditation during this encounter is during the 2nd or 3rd round of Glacial Spikes blowing up.
Sigil of Chains can be useful to grip Frostbound Devoted add together.
Sigil of Misery can be used to stop the Fixate from Frostbound Devoted adds, when the fear ends they will begin their Fixate cast again allowing you to keep them stationary for a prolonged period of time.
Sigil of Silence DOES NOT work to interrupt the Banshees.
Blessing of Freedom can be used to remove the root from Frost Blast.
Blessing of Spellwarding can be placed on a player to allow them to solo soak Frost Blast.
If you are a Kyrian Paladin Divine Toll will interrupt Banshees allowing you to interrupt multiple at once.
Frostbound Devoted can be stunned with Shockwave and they will begin their Fixate cast again when the stun is over allowing you to keep a group of them stationary for a long time with a single stun.
Ice Shard is blockable.
Spell Reflection is best used when the Glacial Spikes are blowing up to mitigate damage taken.
Rallying Cry is best used to help the raid whilst the Glacial Spikes are blowing up.
Shapeshifting will remove the root from Frost Blast.
Stampeding Roar is useful to get players together for Glacial Spikes.
Anti-Magic Shell can be used to avoid the root from soaking Frost Blast & Wraith Walk will remove it.
Anti-Magic Shell can be used to immune stack(s) from the Glacial Spikes blowing up.
Anti-Magic Zone is best used to mitigate raid damage taken from the Glacial Spikes blowing up.
Gorefriend's Grasp can be useful to grip Frostbound Devoted adds together.
If you are a Necrolord Death Knight be careful when using Abomination Limb whilst Frostbound Devoted are active as you could grip the one fixated on you to you and blow up the raid.