Things I liked:
-It's overall fun to play
-The art is amazing
-The SFX give it a really nice touch and ambience
-The metreoidvania genre is well applied
Things I didn't like:
-The controls are floaty, it would fit with the underwater environment, but it's too much
-The Shell is quite slow and sometimes the parry doesn't work
-The platforms are really small, which makes it hard not to be hit and not to fall every two seconds
-Some buttons, as you stated, don't work
It was fun, and I hope you continue developing this