Unholy Death Knight

Legendary: deadliest coil

Legendary: deadliest coil

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

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

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

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.

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: deadliest coil

You would want to go clawing shadows on the boss since you will be running out of melee range quite often when the boss slams into a pillar he will take increased damage so make sure to use every available cooldown when that happens.

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. 

When shattering blast is being cast, use death’s advance to avoid the push back.

In the first phase it’s a single target focus with 4 sets of adds spawning. Make sure to prioritise the adds whenever they spawn and use epidemic on 3 or more targets.