Aliens(UFO) Invasion (외계인 UFO의 침공을 막아라)

ㅇ The aliens(UFO) are coming down from the sky to destroy the earth. We have to stop them.

ㅇ We have to avoid the aliens' bullets and fire them and destroy them.

ㅇ The more you destroy a large UFO, the higher your score

ㅇ After one step, we move on to the next, more difficult step.