Cool little game! I loved the design of the protagonist and the whole idea of playing as a ghost. (She actually reminded me of a sea angel, not sure if intended or not!)
The level backgrounds were gorgeous, and overall the underwater atmosphere was great, though the solid black tile edges looked a bit out of place sometimes. The music kicking in late and the transition from dark to light were a neat touch, too!
The movement felt sufficiently underwater-y, and I liked the amount of jump distance you could get. The dash ability is a cool concept, and chaining big leaps together felt satisfying! However, the hitboxes for launching in each specific direction were pretty small, and it was easy to send yourself downwards or in the wrong direction. Some of the runbacks after falling down were pretty long, and having to change rooms in order to respawn enemies to dash off of was a bit annoying at times, too. I think the dash ability might work better if it could only send you up, not down, and perhaps was based on player facing rather than position. The wall climbing ability looked really cool and worked well, though the recovery on the flight ability felt a bit long, and flight in general kinda felt like just a more cumbersome double jump.
Dealing with enemies was a bit hard due to the small hitboxes making it hard to hit anything without getting hit, and after a while, I resorted to avoiding enemies when possible. Also, the dash sometimes seemed to go through enemies without harming them. On the other hand, it looked like the enemy movement was based on the center of its body, but only the head did damage. Meaning that once the enemy was on top of you, it'd just get stuck there spinning back and forth and not being able to hit you.
The reused witch at the end was pretty funny! I'd love to see what an actual boss might look like with this kind of movement and combat mechanics, though. Overall, very nice job!