Finding yourself in a small arena, you face a lot of enemies. When you kill them, you get money, which must be spent to buy new weapons and items. Upgrade your character and keep track of his progress. You have to try not to die before the end of the wave, so watch the timer carefully. Between waves, you’ll have a store with different guns and other valuable items, like knives, books, alien tongues, gears, or toxic liquids. Several of the same weapons can turn into one of higher quality.