This was really fun! The bubble attack felt unique and fun to use, especially since I could spam it. To balance that, it might be worth it to increase enemy HP a smidge? Most of my enemy encounters ended pretty quickly, even in large amounts, so more enemy HP could maybe balance that. I also think dying immediately when hitting spikes is a bit harsh, especially since there's not too many save points scattered around. I also didn't realize I needed to press Load Save after dying, so for a bit I kept starting new playthroughs! A quick prompt on the menu could clear that up.
As a metroidvania, I really like the mechanics! The bubbles floating up is especially unique, and I love how all the abilities are toggleable. I also enjoyed the first boss, really surprised when I saw it for the first time! The boss itself was also designed quite well, and it's attacks looked really polished. Unfortunately, I got lost and didn't now how to proceed after getting floating bubbles. I wish I could have gotten further, but you have a lot of neat stuff here! Congrats!