I played the full demo (up to the "BOSS UNDER CONSTRUCTION" message).
Overall it's pretty good. It's nice to look at and to listen to, controls well and the difficulty of the plateforming phases we get to play here especially is pretty much perfect.
I don't know if it's meant to be structured around losing all your abilities once in a while or if the first part is a tutorial, I've no strong opinion about it but that'd be unusual, it's interesting.
I'm not sure about the design of the slime boss with just more and more bubbles coming and then you pretty much need to immediately reach it twice and deal two damage each time or you're doomed, just as is with no other twist it doesn't feel that great although it was satisfying to beat it.
Thanks for sharing, keep up the good work!