You can move Bud (the little green alien) through 2D scenarios where the objective is to capture a certain number of zombies. To capture a zombie, you just hit him with a harpoon. But watch out, because a lot of zombies hide, so you have to use bait to get them to come out.
Once the zombies are captured, Bud and A.J. get the business running by making zombie smoothies. Yes, smoothies. With the proceeds you earn from the sale of these smoothies, you can buy better equipment, adding new weapons, bait, and even a jetpack.