Ok what you have here is brilliant! Great effort. You have really nailed the theme. I managed the finish the game and was actually disappointed that there weren't more levels. The only things I would change is when you on the other side make up arrow ground pound instead of down, it makes more sense as everything else is inverted. I also don't think you need the walking animation, I think it would have worked better with a simple white cube with some squash and stretch on it to make it feel squishy. These are minor things though so well done!
I'm glad that you liked the game!! Thanks For Playing!! Ye I'm sad too that the game is very short :C
It originally was like you suggested (inverted up/down controls for the upside down player), but it was really unintuitive and a lot harder to control, so i change it to the way that it is now!!
And about the walking animation... Maybe you're right, but i really like how it turned out the character, so i don't think I'll change it (^u^)
Still, Thanks for the feedback!! Really Appreciated!!(^D^)