Music is by csx42 if you're interested! I see what you mean by challenges, kind of like the comet in mario galaxy, and while I think it would be a cool addition, it would kinda break the feel of always going forward, if this were to become a full game, you would never be able to backtrack, because, well, you can't go back! However I could add a hard mode for after you complete the game normally which makes you replay everything with new challenges, actually this may be what you meant, but yeah, I'll see if we continue this, that could be fun!
I feel like The Grave Warning fits more there personally because I kind of wanted to personify the grave, but well, that sounds weird in the end thats true^^