Fun game! I appreciated the controls and that there is feedback/knockback when you hit enemies. The palette is very unique as well and feels whimsical, and the sword slashes on-screen are cool (I like that there's even a combo!)
Besides the difficulty in progression I have some other feedback on difficulty:
The camera moves in a way that doesn't let you see what's coming up ahead, it would be helpful for the camera to pull forward to see upcoming enemies.
Also the projectile enemies aggro on you while off-screen, which leads to a lot of unavoidable (for me anyways) damage.
That all aside, it feels like the elements of the game were put together with care. Great job!