Unlimited health. All purchases add more.
You are the super heroes who use to conduct many missions for the Earth in the space. But now your ship has been crashed and you need to park in onto a strange planet, which is full of the wandering zombies. Hell is coming. Use all the weapons you have here to stop them from mooing toward you and your ship. Shoot at will, Try to get head shot to kill them easier. The longer you can withstand them, the more advantages you will have with the money you gain from their deaths. With that money you can buy and upgrade your weapons for further fights with the zombies. You can always have the feeling of trying the new weapons onto the enemies in the later levels, supposing that you can survive all the levels here.