My absolute favourite game so far, I adore the idea and execution! I my only gripe is that there is no pulling mechanic for the box so you can soft-lock yourself by pushing it all the way to a corner when you needed to go the other direction (happened to me on the third level).
Otherwise I loved the bold spritework and the driving music. I appreciated the attention to detail in making each character feel unique between the mechanics, animations and abilities. I flashed a smile when I realised the younger version could jump much higher, it's the small things that make you connect with the game in a deeper level. By the end when you're switching mid-air it has a great game-feel. If you guys ever feel like expanding it into a full game please make a ROM so I can play this on hardware.
Great job!