I feel like you made a simple game exactly how you wanted it, so I don't know what to say, but (playing on hard) it initially feels like the enemies have more going on that you'd expect for the simple presentation, the way they mix up a challenging moveset, so I'm like, "huh?" But when I learned everything I could do it felt a lot better to play. Some enemies like the knight and red bird are hard to kill with slashes but fairly easy but stomping on them, but I didn't know I could do that until I checked the controls, which I didn't expect I'd need to do for a game that looks like this. In the end I killed the pale dragon by using the jump spell to get on her head after facing her into the corner, staying on the right side so she'd be stuck there. She did a swooping move into the side of the screen and glitched out and got stuck -I don't even think that's a bad thing in any way, it was hilarious and rewarding.
I hate to suggest tutorialization, but maybe you should add some way to get people into stomping, and make sure they know how to cast magic. Or not, the difficulty option is there for a reason. I'm also not sure on the charge-slash in how you can cancel it by moving. Usually when a game has a charge move like that I want to step forward and throw it out while buffering a movement, but needing to make sure im not pressing any keys when I want to use it makes it feel clunky to time. It seems like rapid slashes are better for damage anyways, so I never used it against snails.