Hold shift to activate super cannons! (Uses 5 ammo per shot!)
Hold control to activate mega cannons! (Uses 40 ammo per shot!)
You gain 1 ammo per second, but much more if you can manage to land the meteors on the grassy plains next to your city!
The darker a meteor is, the more dense (and more difficult to deflect) it is! It also gains you more ammo if you land it!