Hmm... this isn't really a "challenge" or anything, per se, but you know how when you activate a launch star in Galaxy, it throws the little harp part in there that's in key with the song, etc. (and is longer when you activate a bigger launch star to go to a different planetoid)?
Well, I was thinking it'd be really cool if alllllll those parts could be recorded and edited together so that entire song has that going on in it.