Pause the game while on the Mothership, then hold L and press Black(2), White(2), L, R, L, R, White, Black.
Alien From Ipanema mode
Pause the game, then hold L and press Y, Black, L(2), White.
Ammo-A-Plenty (infinite ammunition)
Pause the game, then hold L and press Left, Y, White, Right, Black, X.
Aware Like A Fox (full awareness)
Pause the game, then hold L and press R, X, White, Black, R, White.
Better DNA value
Every chance you get, do not kill a human before you extract their brain stem. Extract their brain stem first as it will make the DNA worth more (25 instead of 10). The easiest humans to do this to are the scientists in the level with glowing cows. For some reason, if the person that is important to you dies (the person you need to abduct), extract their brain stem before you return to the Mothership -- the DNA is usually worth more. Additionally, it is rare to find humans with brain stems that are worth 50 or 100 DNA. Most humans have brain stems that are only worth 10 or 25 DNA. If you walk around Union Town, there will be humans with signs on them reading, "REPENT THE END IS NEAR". Those humans will have a brain stem worth 50 DNA. Also, Mystery Agents' brain stems are worth 25 DNA points most of the time, whether dead or not.
Blind Humans
Pause the game, then hold L and press White, Black, R, Left, X, Black, White.
B-Movie Theater bonuses
Complete the indicated level to unlock the corresponding movie under the B-Movie Theater option.
Bulletproof Crypto (invincibility)
Pause the game, then hold L and press X, Y, Left(2), Y, X when you are Crypto.
Control objects
When you pick something up, you can control it with the Right Analog-stick.
Deep Thinker (infinite concentration)
Pause the game, then hold L and press Black, White, Y, Right, White, Y. Your concentration meter must be above 0% or you will not be able to use any of your mental abilities.
Destroying Majestic cars
Use your PK ability on a Majestic limo; hold L the whole time. Get a wall between you and the car, then start running away from the wall until the car smashes into it. Keep running backwards and the car will eventually explode. This trick can also be used to take out normal cars and people.
Easy collect brain stem puzzles
Enter a collect brain stem puzzle and find out how many brain stems you need. Then, stand around and extract the brains and leave them laying close by. When you have enough, go to the challenge and enter it; you can easily win by doing this.
Extra jetpack distance
While using the jetpack, quickly tap A to go farther distances.
Extra robot arm
When done with a mission at the capital city, enable the "Deep Thinker" and "Bulletproof Crypto" codes. Go to the bridge that goes to the octagon. Attack the people to get the robots to attack you. Use the mind control on the robots and lay them about over the edge. You can see a robot arm pulling the robot into the water.
Extract DNA faster
While extracting a person's brain stem (alive or dead), quickly tap B. You will get their DNA easier. This is useful against the M Agents and Psi G-Men.
Faster Destruction in the UFO
Instead of holding R to destroy buildings or large objects, tap R and the destruction will happen faster without waiting for the recharge.
Finding more probes
Probes are necessary to get upgrades quicker. In order to find them all, make sure to look high up on rocks or hard to reach places. Your jetpack is essential in getting to the high places. You may have to get up on the ledge or building, then use your jetpack to fly higher to get the probe.
Flowers For Algernon reference
If you scan a Psi-Mutant a few times, he will say "Algernon... Good mouse... Smarter... than... Charley". The Psi-Mutant is thinking about the book, "Flowers For Algernon".
Furon Down!: Furon Down!
Outro Movie: Attack Of The 50 ft. President
Plan 9 from Outer Space: Teenage Zombies from Outer Space
Teenagers from Outer Space: Attack Of The 50 ft. President
Furon Propaganda bonuses
Complete the Attack Of The 50 ft. President level to unlock the following entries under the Furon Propaganda option: Crypto, Phone Home!, Developer Darwinism: Evolution Of The Game, E3 Booth Footage, and Goofy Screenshots And Voice-Overs.
Furongami movies
Collect all the probes in the indicated side mission to unlock the corresponding movie in the "Furonigami" option under the Archives menu:
Art Of The Furon: Santa Modesta
Blue Book: Saucer Blueprints: Rockwell
Evolution Of An Alien: Turnipseed Farm
Face of the Enemy: Area-42
Pathetic Humans!: Union Town
The Concept Barnyard: Capitol City
Get on Santa Modesta tower
To get on top of the Santa Modesta's SMCBS TV station towers, first get on top of the station's roof. Then, jump onto the satellite dish and from there, to the slim post. Once on the post, jump and use the "Extra jetpack distance" trick to reach tower 2. From tower 2 you can also go to the other tower. From that altitude the police, army, and Majestic cannot see you. Use the Ion Detonator to blow them up. This is best done when aiming down before jumping; you can then see where you are landing.
Getting away from the law
Don't bother trying to run away from the authorities with short legs; use your jetpack liberally to fly away. Press Left Analog-stick Forward and hold A to boost away.
Helvetica mode
Pause the game, then hold L and press Black, White, Black, X, Black, White(2).
HoloBob
Put your target (dot in the middle of the screen) on any human, and press B. In order to maintain your HoloBob, you must read the thoughts of the humans walking around. You can read the same person's thoughts repeatedly to keep your mental powers charged.
Hypnotize faster
When trying to hypnotize people, rapidly tap X.
I Told You I Was Hardcore mode
Pause the game, then hold L and press White(2), R, X, Y, Black, White, Black.
Levitation death
It you levitate a person for a long time, they will die.
Lower brain juice meter
When you are in the form of another person, to make you brain juice meter go down, read other people's thoughts.
Mmm... Brains! (increase DNA)
At the Mothership's main menu, hold L and press Black(2), White(2), Left, Right, Left, Right, White, Black. If you entered the code correctly, a message will appear.
Monkey Brad (annoys FlexMentallo)
Pause the game, then hold L and press White, R, Left, Black, Y, White, Black, X.
Moonwalk
Stand in an open area on any level and walk forward. Keep decreasing your speed until you eventually begin walking in place.
Movies
Collect all the probes in the indicated side mission to unlock the corresponding movie in the Furonigami option under the Archives menu:
Art Of The Furon movie: Santa Modesta side mission
Blue Book : Saucer Blueprints movie: Rockwell side mission
Evolution Of An Alien movie: Turnipseed Farm side mission
Nobody Loves You (no awareness)
Pause the game, then hold L and press White, R, White, Black, X, R.
Plan 9 From Outer Space reference
Halfway through the game you will experience a level where you go to the drive-in to switch films with the one that is showing. Watch what is showing before you switch films to see that the film is Edward D. Wood, Jr.'s Plan 9 From Outer Space.
Pox remarks
Allow the game to idle at the mission selection screen and Pox will make various remarks.
Pox Unlocks (all upgrades)
Pause the game while on the Mothership, then hold L and press X, Y, Left(2), Y, X. All upgrades for the currently unlocked weapons will be available for purchase from Pox's lab.
Ride the Washington Monument
Find the monument, then throw cars at it until it breaks into two pieces. Get on the long pointy piece, PK the middle, and try to stay on.
Screensaver
Allow the game to idle for awhile; eventually the screen will turn black and white and elevator music will play in the background.
Staying human
After getting out of your UFO, aim at a human and press Y. When you have changed into the human, the bar on the top left corner of the screen will go down. When it is all gone, you will change back into an alien. If you want to remain human, turn into a human and while walking around, scan other humans or animals to make the bar on the top left corner stay up.
Super Crypto
Enable the "Bulletproof Crypto", "Ammo-A-Plenty", and "Deep Thinker" codes, then get all of Crypto's upgrades. After this you can turn into a human and walk around TK'ing everything.
Super saucer
Enable the "Bulletproof Crypto" and "Ammo-A-Plenty" codes while on your saucer. It will not get damaged or lose ammunition.