It took a little bit of luck, and burning through more resources than I'd like, but I managed to beat him. The biggest motherfucker was the move where he throws a bag of Clams because it always deals a set 200 damage regardless of stat changes, so if it hits Sunny or Kel you're just dead, I almost lost this run to it near the end but luckily Sunny still had his "did not succumb" effect.