I think I'll pass on this one. I'm curious to see what other people will make, but 20x15 has never been that interesting in my experience. I can think of a few neat ideas for a tiny level, but they'd all need to be a little bit bigger than one screen. As it is, these rules are just too restrictive to make anything that's worth playing.

This seems like a contest geared towards levels that look cool, rather than ones that play well. FS's point about puzzles also applies, but I doubt said puzzles would be very sophisticated.