Simple Santa: AI override unkillable
Speeds: Sir Nicholas 233, FB 179, Doompriest 167, Suwei 166, Fenshi 107
With the ability to turn off Santa's A2, he can provide all the unkillable you need by himself.
Things to note:
Everyone but the stun target must have lifedrinker mastery.
Santa's continuous heal will bring the stun target to 17.25% heatlth (enough that the boss doesn't recognize the unkillable), but the poison from the boss' A1 will drive it under that. So you need a cleanser (doompriest in this case), or a block debuffs
Don't pick the mastery that can extend Santa's heals (it will lead to a double heal on the stun target and mess it up)
As usual, no turn meter boosting masteries or abilities.
I'm only early mid game and will figure out UNM by the time my clan unlocks it.