I just finished playing your game! I LOVE this idea.
Doing a bunch of random tasks together with someone else and trying to get the timing right. This could be a lotttttt of fun. I am reminded of Wario wares style games. A bunch of quick, super crazy mini-games, but this time, we are talking about teamwork.
I'd say add some music to each of the existing levels and start pumping out more levels. You could also add some avatars at the top of the screen with three different emotes, normal, happy, and sad/mad. That will give the player another visual reward for completing the challenge.