I'm in the same boat. Currently working on a little multiplayer proof of concept for the jam. What I'm doing to ensure that, despite it being multiplayer, it can be judged without requiring a player 2 is creating a "level 0" which doubles as a single player tutorial to show players the ropes and give them an idea of how it works. Maybe try creating a rudimentary state-machine that a single player can play against?
Good luck with the game!