Select "Options" at the main menu and "Cheat", then activate the following cheats by entering the corresponding codes. Note: Enabling codes will disable game saves. that you will be unable to save upon activation:
CHEAT FUNCTION - CHEAT CODE
Level select - RMTE
All characters in multiplayer mode - CAST
All costumes - WRDB
One shot kills - MNKY
All weapons in multi-player mode - DKSD
All weapons in single player mode - GTSM
Maximum money - PWTR
Unlimited ammunition - GGTY
Head Shot - Kill an enemy with a single shot to the head.
One Shot Kills - Successfully kill an enemy with one shot.
Multi-Kill - Perform a multi-kill with a melee weapon.
Multi-kill with a grenade - Perform a multi-kill with a grenade.
First Kill - Successfully complete your first kill of an opposing team member in Multiplayer.
Roadhouse - Kill 3 members of the opposing team with a melee attack before you die in Multiplayer.
It's All Greek To Me - Complete the "It's All Greek To Me" level.
Something's Amish - Complete the "Something's Amish" level.
Handicapable - Complete the "Handicapable" level.
Pussy Whipped - Complete the "Pussy Whipped" level.
No Cheese, Please - Complete the "No Cheese, Please" level.
Long John Peter - Complete the "Long John Peter" level.
Santa's Sweatshop - Complete the "Santa's Sweatshop" level.
Chickens In Space - Complete the "Chickens In Space" level.
Chicken Fight! - Complete the "Chicken Fight!" level.
We Be Clubbing - Defeat 10 enemies with a melee weapon.
Lockdown - Shut out the other team from scoring in Capture the Greased-Up Deaf Guy.
Mr. Unpopular - Choose Meg for a Multiplayer match.
Teabaggin' - Taunt 25 times in any Multiplayer match.
IEDead - Kill 60 enemies with grenades/explosives.
Help From My Friends - Use the collectible special inventory items 25 times in Story Mode.
Boom Headshot - Kill 75 enemies with headshots.
Bipolar - Switch between Brian and Stewie 10 times in Story Mode.
Shut Up Meg - Kill Meg during any Multiplayer Match.
Scorched Earth - Burn the pot fields in the "Something's Amish" level.
How Do I Jump? - Kill yourself with a grenade or satchel charge.
Kings of Quahog - Win a Deathmatch mode (free-for-all or as a team).
Bestest Infiltrator - Win an Infiltration map.
Grease Can't Save You Now - Win a Capture the "Greased-Up Deaf Guy" match.
Teabag a D-Bag - Taunt a dead opponent with Quagmire in Multiplayer.
Little Dipper - Earn 10 stars in Challenge mode.
Bird is the Word - Taunt 5 times in a row with Peter.
Ugly Tastes Terrible - Play poorly during the final showdown.
Bunch of Chumps - Survive 15 waves in Multiverse Madness.
Wrecking Ball - Smash your opponent into something 20 times in the "Chicken Fight!" level.
Pervert - Hang around the room with Quagmire in a baby costume for 30 seconds.
Employee of the Month - Kill Vernon.
Day Labor - Destroy all of the piņatas in the "It's All Greek to Me" level.
Penny Pincher - 4Collect $50,000 in Story Mode.
The Cleaner - 4Get a 10 kill streak in Deathmatch.
Mort Will Now Lend You Credit - 4Buy everything available in Store.
Stewie-nator - 4Kill 500 enemies using Stewie.
Justified - 4Kill 500 enemies using Brian.
Big Dipper - 4Earn 21 stars in Challenge mode.
Cartoon Apocalypse - 4Survive 30 waves in Multiverse Madness.
No Place Like Home - Complete the "No Place Like Home" level.
Obsessed - Complete all secondary objectives.
There is no Cake - Earn all Bronze, Silver, and Gold trophies.