Great job on the game, I had a lot of fun with it. I'm glad to see that you plan on updating it soon and I'm excited to see what's coming next, it's a very strong start.
My only recommendations for improvements in the base gameplay would be faster enemy attacks, especially the boss, and maybe making things a bit faster in general if possible. While the movement is good and pretty fast once you get going, combat itself is in a weird place when it comes to speed. Other than that, maybe making just crabs drop health to be a bit more thematic, but I don't know how that'd be received. I was also thinking that maybe the crystal could have another use, such as being a bomb when it expires.
Not many issues were presented during gameplay. Pulling with the grapple is a little funky; when you're standing, you seem to want to go upwards rather than forwards, but it's fine when done in the air. Pulling is also interrupted sometimes when side-bumping things, but I don't know if that's intentional or not, similarly to spikes being triggered by coins, gems and health and enemies often dying to traps. Barring those, I got stuck on a pot, once.
Didn't have any performance issues, myself, but I've got a pretty good setup so it could just be me. I keep it at 60 FPS and it stays there no matter what.
Thanks for the game! I'm pretty hopeful for its future.
About enemies, we hope the combat gets more interesting when we add more enemies. Enemies dying from traps has a side effect of balancing some rooms, where there would normally be too many enemies to deal with by hand. Traps getting set off by crystals can be used strategically to kill something without getting close, and to watch out where you throw your stuff as not to jump straight into spikes.