Good job. I really like it, I'm surprised to see that many types of enemies, I also like how the music changes the deeper you go.
The movement felt smooth.
I like how the trail of bubbles only appears for a second after you start moving and throughout the entire swim cycle, was that intentional or that's just how it came to be?
I just feel like the movement could use a bit more of acceleration and friction.
Also there was no air resistance but I understand that this might be intentional given the nature of the game (always falling down and need to move quickly while falling).
While you're falling down you shouldn't be able to double jump (you should have just the second jump meaning that you lose the first jump even if you haven't used it).
I found a chest that animates when I come near it and had what seems to be gold inside it, can I interact with it?
