Really fun mechanics !
I like that you constantly fight not only the boss but also your ground on the arena since you can destroy the blocks the enemy can place, the opportunities to upgrade in between phases in the fight is also a nice detail.
The difficulty ramps up a bit quick though, as i found it to become quite hard when the enemy started shooting the bouncy projectiles, however i gotta point out that the checkpoint to not start all over is a really good quality of life feature to have.
Overall good job :)