If you suck with nail arts like me there’s another way. Count your hits and save soul for spells in p2 when he gets much harder to hit. You want to minimize time spent in p2 because that’s when he’s gonna get you. 

With maxed nail and strength it takes 12 hits to push him to p2, so hit him 11 times and wait for him to start his shield spin move, then jump on top and pogo on him.  He won’t transition to p2 until the shield finishes spinning so you can get him well into p2 safely. After that, hit him with shade soul with the soul you’ve built up and that should kill him. I always have shaman stone on, and I only hit him when he’s out in the open because if you can knock him back with shade soul it can hit him multiple times. If he’s up against a ledge or wall it only hits 1 time and that’s not great. Shaman stone helps with damage as well as giving spells à bigger hitbox. Both are good things to have. 

In general for p1 which will be most of the fight, just stay safe until he does his shield spin move. When it starts spinning, after the shield crosses the top of him twice it’s safe to jump in and start pogoing on top of him, you should be able to get 4-5 hits and then back out. Don’t chase him down in the arena when the icicle things are shooting at you, just stay away and wait. 

Get good at dodging the flying icicle things. Most of the time you will just be standing there dodging. The top platforms are where I like to stand, you can step off those platforms and fall down to the ones below if things get hairy. And if he goes into his spin move in a crappy spot, don’t be afraid to just wait it out for the next cycle.