Mythic Boss Rush Lvl 380 Undead Onyxia First Boss

How do you beat it? I tried Bwonsamdi, Khadgar, Balinda + Cookie, Varden, Geddon, but they die around turn 5+, when i leave only Balinda, Geddon Khadgar, Onyxia's abilities pummel them.

What other comp i can use to pass this boss? Balinda, Khad, Varden, Cookie, Geddon are maxxed, around 40+ levels each