SUPER charming gameboy style, I loved the use of the theme and the addition of the final bosses weapons on replay was a great addition, definitely one of my favourite entries I ended up playing it twice, great job!
Small criticisms
I'd maybe be a bit more generous with hitboxes, also seems like usually the most effective strategy for bosses is to tank hits and keep attacking, though hard mode slightly remedies this. I think the easiest way to stop this would be to add a bit of knockback when the player hits a boss with a melee attack.