It's a gamejam so we can be forgiving about platform feel, but this one is a bit awkward feeling; it takes away from the fun :(.
A 2d platformer with 2 worlds that you switch between is the obvious choice for this theme. Your "other" world is not so different from the first world... but the fact that the main character runs off and you get left behind as a ghost was very... compelling for me. Very interesting.