This is for the most part your baseline Patchwerk fight with occasional priority targets and cleave.
You can keep stacks of Storm, Earth, and Fire for Waning Time Particles (priority targets). Don’t forget your clones will jump on fragmented time particles if you don’t fixate them on one target, keep making sure they’re hitting the right thing.
This is a very straightforward fight, dodge every void zone you can possibly spot. You can transcendance over the waves, transcendance back to boss after going out for Time Bomb. Monk’s mobility is highly appreciated.
If your raid is pushing the channel of Power Overwhelming in Phase 2, you can spec into Diffuse Magic and use it later on in the cast to survive easily a large tick. Otherwise Healing Elixir is the go-to talent.
Mythic Chronomatic doesn’t add any new mechanic but enhances all of the ones you deal with on heroic. Adds now spawn two at a time and require your raid to split up in two groups, usually one big and one small, to deal with them.
Windwalker is very good at doing that job if required, with interrupt, leg sweep to stun small adds, arcane torrent if you are blood elf.
Use your touch of death on cooldown, and the third one should line up with the “difficult” spawn of adds during slow time. This is the best place to use it if you’re progressing this fight.
Put transcendance whenever you can and keep in mind where it is.
As mentioned, Gale Burst has a weird interaction with Passage of Time mechanics in Nighthold as it is not a periodic damage source and is not a buff on you, so it doesn’t usually get affected. This means for the first time your Gale Burst can be more or less GCDs worth of damage depending on which phase you’re going through. Be aware of that, but don’t overreact.
Being swift to move through mechanics and Time Bomb is part of what makes Monk very smooth on this fight.
As said before, be careful with Fragmented Time Particles: although it is great to pick up 5 stacks of mark of the crane and cleave, you don’t want your clones to start wasting Rising Sun Kick on these. Make sure you’re aware of what you do with Storm, Earth, and Fire.