Really liked the mechanics and the frequent checkpoints! One way to improve is the instructions in the beginning are wrong, it should press Z to jump, and also it doesn't mention to press z and down to go down from platforms which is required very early on. I wonder if it should be mentioned on the itch.io page as it could be confusing.
I could not get past the part that had the spikes on the left and right for some reason, ironically it might not even be that hard of a part but for some reason I couldn't figure it out. I might consider to try it again and see if I could do it. But overall, really nice job on the game!