Fullscreen is fine but it cut off some region ( zoom to center while on menu, character while in game ) without that.

The character is so cute and I like this sort of art, but after that, almost nothing is playable, maybe there have some bug ?

first, no any checkpoint, I think this include in your design, but at least I can't  found any on the map.
it's actual difficult to do any play test without that, because I need to restart on start position every time.
second, camera is... buggy ?
camera can not follow player if I fall down from a high platform, until I landing on the ground.
even I haven't fall, camera sometime shifted up / down while I swimming in water ( I move up and down quickly ), it make me difficult to dodge squid bullet.
and... is there any problem of character jumping height or horizontal distance ?
my character can't jump over the first squid with any "Normal" method.
but I can stick to the wall and continuously hitting jump key than it can magically climb up.
I have success to do that twice, but I don't want to test any more...

I think this is... a bug report.
I love the art and concept, hopefully to see a playable version later.

That character is so delightful! I really like the concept but there where a number of challenges so I wasn’t able to get very far. Player hitbox feels really big and/or bad timing, I’d swing attack and the crab would fall apart but I’d still lose health. I don’t know how I managed to jump over the first squid gun but I wasn’t able to get it every time, and once got stuck in the at pit, unable to move at all. It got to the room where you start at the top and move down the water on the left, trying to time past the squid guns but the laggy camera meant I got hit, fell uncontrollably getting hit a second time and landed with one health left, which I soon lost.

This really oozes charm and I think the mechanic could lead to a lot of cool things (I’m curious if you had some other ideas), definitely want to see more after some of the jankiness is dealt with. Also desperately wanted controller support!

That creature is peak cuteness. Not a bad game, you should add a picture to the entry. The camera doesn't quite follow the creature, but otherwise it's pretty good.