With the knowledge you've gained from this guide, you might take a stab at unlocking the various cheat codes contained within the game. Keep in mind that these codes are just for fun; none of these cheat codes actually allow you to beat the game any easier. In fact, to even use these codes, you're required to beat certain levels under certain conditions. It's a lot of work, but if you've studied the walkthrough and the strategies for each species, you shouldn't have too much trouble.

Once you've unlocked a code, you'll notice another main menu item marked "Cheat Options". Select this option and you'll find a list of the various cheats you've uncovered. From here, you also select the level in which to use the cheat. Keep in mind that most codes are species-specific. For instance, the "PIGSTICKING" code that gives the Predator a beefed-up speargun can only be used on Predator levels.

Below you'll find a sample list of cheats, what the cheat does, and how to unlock the code. Before you're able to utilize the cheat, you must unlock the code by beating the particular level under the conditions mentioned.

SUPERMUN: Alien gains long-distance jaw attack. To acquire the SUPERMUN, you must defeat the first Alien level, Temple, and score 10 live civilian head bites.

NAUSEA: The entire screen shakes and moves, causing, well, nausea. To acquire NAUSEA, you must defeat the second Alien level, Escape, in less than two minutes.

PIPECLEANER: All characters are shown as pipecleaners, or as their skeletons. To acquire PIPECLEANER, you must defeat the third Alien level, Ferarco, with 15 dead civilian head bites.

MOTIONBLUR: Makes the screen blurry. To acquire MOTIONBLUR, you must defeat the fourth Alien level, Gateway, in under four and a half minutes with an average speed of 9 m/s or greater.

MIRROR: Mirrors your display of the level. To acquire MIRROR, you must defeat the fifth Alien level, Earthbound, with one live Predator head bite.

JOHNWOOMODE: When you attack or are attacked, the game slows down. To acquire JOHNWOOMODE, you must defeat the first Marine level, Derelict, with 80 percent head shots.

GRENADE: Stocks your Pulse Rifle with 99 grenades (but no bullets). To acquire GRENADE, you must defeat the second Marine level, Colony, with 40 percent accuracy.

WARPSPEED: Run very fast. To acquire WARPSPEED, you must defeat the third Marine level, Invasion, in less than four minutes.

LANDOFTHEGIANTS: Makes you very small. To acquire LANDOFTHEGIANTS, you must defeat the fourth Marine level, Orbital, using less than 20 shots.

SLUGTRAIL: Causes all Aliens to crawl on the floor because they have no legs. To acquire SLUGTRAIL, you must defeat the fifth Marine level, Tyrargo, with 32 Alien kills.

PIGSTICKING: Gives the Predator's speargun unlimited ammo and extra shots. To acquire PIGSTICKING, you must defeat the first Predator level, Waterfall, with 80 percent accuracy.

SUPERGORE: Ups the level of blood and gore. To acquire SUPERGORE, you must defeat the second Predator level, Area 52, with 25 marine trophies.

BALLSOFFIRE: Enemies are always on fire. To acquire BALLSOFFIRE, you must defeat the fourth Predator level, Fury 161, with 40 Alien kills.

RAINBOWBLOOD: Causes the lights, smoke and blood effects to be rainbows. To acquire RAINBOWBLOOD, you must defeat the fifth Predator level, Caverns, and be spotted less than 15 times.

IMPOSSIBLEMISSION: Causes the game to be more difficult because you take more damage. To acquire IMPOSSIBLEMISSION, you must defeat the second Alien bonus level with 20 live marine head bites.

TICKERTAPE: Aliens all have a trail following them. To acquire TICKERTAPE, you must defeat the first Predator bonus level, Invasion, with 15 alien trophies.

TRIPTASTIC: Causes the screen to be blurry, jittering, and rainbow. To acquire TRIPTASTIC, you must defeat the second Predator bonus level, Escape, with 10 civilian trophies.