In Combo X999 you're playing a space invader styles game while playing slot machines. Sounds like a strange combo but the slot machines work in your favor. Use the A button to shoot your weapons and kill as much as you can. The only way to die is to let the creatures at the top of the screen get all the way down and touch you. As you kill, you'll gain credits. Once you get enough credits, press the S button and if your slot machine comes up with three of a kind, you'll get certain power-ups to help you boost your score and fire power. Sometimes your enemies get the power-ups!