For sure this game fits perfectly the theme you chose, smart idea.
I don’t know if that’s a personal choice, but I found a little hard to shoot the enemies, because the ammo (coin) is more or less the same size of the bats. Maybe if it were a little bigger it would be cooler 🤓.
Anyway, good job with this one, I know the difficulty is part of gameplay and that worked very well in your game. Maybe a little background music would make it even more enjoyable 😁.