Take down the incoming waves of enemy troops before they overwhelm you. When using the default weapon, you don't have to worry about ammo. Just click and hold to build up power, then release to shoot. Keep track of your fuel by watching the red meter in the top left. Shoot the tanks of gas to replenish your fuel, and the letters to pick up extra ammo for your special weapons.At the end of each wave, your partner will swing by and give you back some health. If your health runs out and no lives are left, the battle is over!