How to play:
Move your airplane around the screen with your finger.
Try to destroy at least one starship before it reaches the bottom, because if you don't, you'll lose one life.
You get credits for every starship you destroy. But the amount of money you get depends on the color of the ship and the wave in which you've destroyed it.
The color of the shit indicates ships strength. red > purple > blue > green.
Green ship is weak and isn't difficult to destroy. However, since it's the easiest, it gives you the least amount of money, if you shoot it down.
Destroying ships in later waves will also increase the amount of money you get because they get stronger each wave.
Wave after wave, ships will become more difficult to destroy. Not only because they gain strength, but also because they'll get faster.
In order to survive more waves, you need to buy upgrades. You can upgrade your bullets, fire rate, life span, or increase the amount of money you get per kill.
