Standing still, holding up and clicking fast will get the character stuck in the attack animation until you move again. You can just hold in dash all the time, while it drains your HP it never actually kills you itself. It made the boss very easy because it seems like he couldn't hurt you at all then. Nice QTE animation. Good start.
Jumping into the side of platforms does some weird stuff: https://files.catbox.moe/0ykkza.webm