Unholy Death Knight

Legendary: deadliest coil

Legendary: deadliest coil

Legendary: deadliest coil can be used here, but Frenzied monstrosity will likely be better. 

DoT the adds with unholy blight / outbreak and use epidemic on 3 or more targets.

Talenting Death’s reach here is really important to get the extra range on the death grip used to get the phoenixes as far away as possible. Depending on your setup, you might be the one handling the CC on them. If so, you're going to grip them as often as possible and make sure they always have chain of ice on them. When done correctly, they shouldn't reach the boss and the fire doesn't get out of control.

Legendary: deadliest coil

When Xy’mox deploys the Stasis traps you can use icebound fortitude to soak up traps in awkward spots and create more room for melee and ranged to stand on.

On Mythic difficulty, the boss gains a new ability called edge of annihilation, drawing in players and then deals damage to all players within 25 yards. With death’s advance you can pretty much just stand still while it's happening or use it as an escape if you do end up being pulled too close to the axe.

Legendary: deadliest coil would be the superior option for this fight.

You can use deaths advance to run out of the drag in (consume) and potentially get a few more seconds of DPS.

Legendary: deadliest coil can be used here, but Frenzied monstrosity is something you could consider.

This is, for the most part, a single target fight, but when the adds spawn make sure you have dark transformation ready and use epidemic on 3 or more targets.

When the boss casts lightly concentrated anima or Highly concentrated anima you can press anti-magic shell to pre-immune the add spawn.

Legendary: deadliest coil

This is a single target fight as you want to kill one boss at a time. Depending on the kill order, you might want to hold your cooldowns for the Fancy footwork buff. If you struggle with uptime on the boss then the clawing shadows talent would definitely be worth considering.

Legendary: Frenzied Monstrosity

Even though Sludgefist is a single target fight you would still want to play Frenzied Monstrosity since it provide more burst damage for the pillars.

Legendary: Deadliest Coil can be used here, but Frenzied Monstrosity will likely be better.

This boss has a lot of adds that need to be dealt with, so you want to cleave off the boss onto the adds with Epidemic and make sure to position yourself and your pet so the chain from Unholy Pact hits the adds and the boss.

Use Anti-Magic Shell whenever you get the Heart Rend / Heart Hemorrhage debuff.

In the first phase it’s a single target focus with 6 sets of adds spawning. Make sure to prioritise the adds whenever they spawn and use Epidemic on 3 or more targets.

You want to use Anti-Magic Shell on every single blood price in p1 you will have to pop it 3-4 seconds before else it won’t line up.