I gave hard mode a try and BOY WAS IT HARD!! It's clear you wanted to push players to their limits.
However, the difficulty curve felt a bit harsh, especially with the first skeleton boss and the frequent slime droplets and bats. It might help to allow players to cancel or change direction during a charge, as lunging into a bat without the ability to adjust felt pretty frustrating. I think if I could have canceled a few lunges or at least changed direction, I might be able to beat it.
Despite the tough gameplay, I did find some fun moments, especially once I figured out some strategies like lunging behind the boss while he went across the screen.
Here were my attempts at the first level, that's as far as I got :