A platformer where there is two state of the world is an interesting idea. The style of the game is very coherent and the hand-drawn art is pretty. But the game could use a bit more time for polishing.
Like others in the comments said it was confusing to having to wait at the first checkpoint. I got stuck there and couldn't figure out what to do as I assumed I would just die when the timer hits 0. And after knowing to wait it's still not fun to just wait around until the world changes.
The controls are a bit slippery with how much spikes there are. There is two types of wall jumps in game: One where you can gain height with just one wall and one where you need two walls to gain height. The level layout implies the former but the wall jump itself is implemented like the latter.
Overall I like the atmosphere, the music and the vibe a lot. Great work on the submission!