Cool! Nice art. I like the vibe going on. If you really want to polish it, it would be cool to have some more parallax layers so it's a bit less flat, and maybe some sway on the vines and such.
As others have mentioned, it would be really nice to have key binding. I'd like to swap my jump and dash keys. The spikes have a very large hitbox and sometimes you hit them when moving away. Celeste actually checks your direction and only kills you if you move toward them, so that might be a nice quality of life tweak.
Some bugs I noticed: Sometimes the run animation gets stuck on when you stop (or at least freezes in a run frame). If you jump up to the top and move left, you can jump off into oblivion and fall forever. In full screen mode, I crash when I alt-tab out then back again.
Level design and checkpoint placement seem very fair so far (haven't finished it yet, as I just jumped into the void and figured I'd post some feedback).