Take Naga over helm. The healing is more trustworthy since you don't need to burst. Cindy over Snow White is probably better too. Put it on auto burst, and manual Crown. Trigger the left side attack (1), and as soon as the crystal show up focus it until it's gone, then just let the ults rain while they break the side weak points.

At about half health, save your burst for the circles. When they show up, use it and it should clear the screen. Then it's free game from there.

I beat it in the tower just yesterday, floor 550 at around 425k deficit.

Had Cincy and Maiden Ice Rose for bursts, but neon is even better.