Cute graphics. In general, I think there needs to be pros and cons from being in skull mode, because right now its a.) only way to kill enemies, b.) much more mobile, c.) removes the startup lag from jumping, and d.) is more fun.
Also yeah either more checkpoints or a better explanation (not in text, but some other way) of gameplay mechanics. I don't know if I arrived that you cant touch red dudes from your gifs or naturally, but long checkpoints are only frustrating if it feels like the reason you died is the games, not yours