This is what I should have presented yesterday. It's actually the one that I feel I'd most likely want to go ahead with after Christmas. It's a bit Thomas Was Alone-y, but with just one character. It's a fairly simple platform game, but the difference is that you can change size (using Up and Down arrow keys).
You'll need to shrink to fit into certain places, but being bigger gives you a stronger jump. Mechanically this prototype isn't great, the jump isn't working properly for a start.