Good day Squizard! I enjoyed this game you've made. The music for the 1st world was a bit grating on my ears, (8-bit and my ears tend not to mix well) but I understand the want for 8-bit music. I'd recommend sticking to 16-bit, rather than tossing in a bit of 8-bit stuff, because the 16-bit style permeating the majority of your work causes the 8-bit to stick out like a sore thumb.
I would like to see a "You Died" screen, or something similar, because death followed by an instant respawn is a bit jarring for a first-time player of this game. Perhaps you could make a toggle for instant respawns rather than just the default? I'd like to hear a different death sfx for the acid pool as a little detail to seal the deal.
I noticed that you intended this game to be speedrun compatible. A detail to improve there would be to allow the player to move to the next world using a key (or any key) on the keyboard, rather than a button on screen that must be left clicked by a mouse.
Overall a good game, but I hope to see it improve!