An old idea I've had since I started playing polytopia. Add a option to toggle "monster spawning" when you create a new game. When on, "monster spawning" allowing nature bunnies to randomly spawn on forest tiles, acting like feral monsters. Nature bunnies don't capture cities, so they would just be obstacles for other tribes. The chance of a nature bunny spawning would be low, and only be able to happen every 5 turns or so. The whole idea adds a x factor to games that could potentially make games more interesting. The idea could be bad in practice though, and seems more like an april fools joke than a real mod. I would make the thing myself, but coding the idea would require C#, which I don't know.
Bunnies could also be changed to look more like monsters, resembling ghosts, goblins or ogres.
Bunny stats would changed too.