Thank you for the feedback. The boss's first attack is supposed to be learnable, but I made it in a rush for the demo so it may be unbalanced. In fact, it's probably the hardest attack on normal. I'll definitely change it in the future.
I took the control scheme from a SNES shooter I played a long time ago. It definitely had a lot more angles, but at my current art and programming knowledge it would be hard to implement more states without it looking weird. That's one of the main issues with the player along with the gravity-defying projectiles. Adding a "slow movement" button would be simple but I don't know how it would synergize with the rest of the controls.
The sword has a constant hitbox, even when it's down, so making it a hold would change how it behaves. Generally I don't want the player to have to use too many keys. The sword is mainly for scoring and making dodging easier. If you didn't need it that means you were too good at the game (or I didn't explain properly how it works.) To be honest, it's very unfinished.