I actually found a glitch, because I had to walk away from my keyboard for a minute or two: at the very first area in the game, if you make too many monsters, some that can't fly can get stuck on the space part near the entrance to the second screen. That is, if they don't actually "spawn" on the ground. It is very unnoticeable though, as most people won't sit by an entrance to another screen as they tend to breakfast lol.
This probably happens elsewhere but didn't check/test it again.
Otherwise I enjoyed this. Good work.