Thanks for playing!
Honestly, you have to be some kind of god to beat this with one person. I tried, and the closest I got was beating easy mode and switching to the plane whenever I needed healing. I thought about implementing a single player mode, but the behavior was too complex for a simple AI to handle.
Although for what it's worth, I do think that playing with only one player really takes away from the asymmetric design and the communication aspect, which is a core part of the game. Even when I played on custom difficulty and made the difficulty actually reasonable, it still really wasn't the same. After all, getting clapped with a buddy > getting clapped alone