I like the art and the overall feel of the game. The sound effects are also nice. Some things I would change:
-There should be a button to instantly end a life cycle of a character, so you don't have to wait till the timer is at 0.
-I don't know if it's fun that you have to jump with one character so the other can jump on top of him and WHILE he's jumping, also jump. You always have to really carefully time this and I think it's too hard to pull of for many people. Just lower the platforms a little, maybe.
Overall, very cool game!