This feels like a neat demo, I think there's a lot of possible ways to expand on this idea. Some sort of danger or obstacle you need to avoid when it's dark might make it more of a challenge, or maps that are a little more maze-like. The mushroom art and character art is well done.
With my screen settings I could still sort of see the outlines of the land even when it was dark - I don't know if that's intentional or not. Nice job!