Nice, a one-button game! I have a special fascination with one-button games because I'm always amazed at how much variety you can get out of a single input.
Something to consider if you do a post-jam build: What if hitting rocks wasn't an instant game over? What if you instead got some invulnerability frames and lost a bit of "heart" instead? Each side could have their own independent invulnerability frame timer so getting hit twice at the same time hurts more than just one person getting hit.