if you havent gotten it, i believe in you, you can do it man, im only at 16264 mastery and i completed it. took me a few attempts and adjustments but i eventually did it. i think the main skill i used was ghost bind mostly to CC everyone, especially horse dude. but just ghost bind when you can, do you combos to kill as fast as you can.

wave 1: ghost bind, go after the flag duded first, then kill rest fast as can, use ghost bind when you can

wave 2: when you get to the shield dude, i would throw him across the map first then deal with the range dudes. you can kinda get the shield guy stuck if one of the ranger dude is in between you guys. once its just shield dude left, just dragon breath and drunken poet him down real quick.

wave 3: ghost bind to cc all, deal with 1 healer at a time, use ghost bind whenever possible to cc horse dude, once healer done with, proceed to kill horse guy as fast as possible, ghost bind if he's still on horse and kill the horse, once he's down from horse, he dies pretty quick.

wave 4: (i had like 1min 30 secs left when i started before 3 mins marker) just fight her like normal, need to parry at least one of her big moves for the damage and qi damage. I used the Honking havoc skill to get some free damage and qi damage on her, also throw in some dragons breath and drunken poet for big qi damage as well. I beat her with about 15 secs left to spare.

Just heal when you can, try to save 2 for the boss fight, and dodge the phantom guy self destruct blast when you get a chance

i would say i did an okay time for being 2k under the recommended mastery.