To access the cheats menu, go to the "Extras" menu and press R2.

Unlock the following costumes by completing the corresponding mini-game with a "C" or better rank:

COSTUME - MINI-GAME
Andy's "Astronaut" costume - Hill Defense
Andy's "Lumberjack" costume - The Gauntlet
Andy's "Pirate" costume - Lava Battle
Andy's "Samurai" costume - Dodgeball
Andy's "Scout" costume - Sort Or Explode
Andy's "Surfer Dude" costume - Jack Attack
Carrie's "Anne" costume - Carnage
Carrie's "Construction Worker" costume - Construction Destruction
Carrie's "Devil" costume - Leprechaun Rouncdup
Carrie's "Forest Girl" costume - Monster Race
Carrie's "Valley Girl" costume - Match 'Em
Jennifer's "Amazon" costume - Monster Onslaught
Jennifer's "Ballerina" costume - Pizza Delivery
Jennifer's "Belly Dancer" costume - Zombie Dance-Off
Jennifer's "Cheerleader" costume - Death School
Jennifer's "French Maid" costume - White Water Swanning
Jennifer's "Nurse" costume - Witch Hunt
Zack's "Cowboy" costume - UFO Shooter
Zack's "Deathgame" costume - Zack-Man
Zack's "Dinosaur" costume - Zombie Cats
Zack's "Scuba" costume - Suburban Warfare
Zack's "Secret Service" costume - Slice N' Dice
Zack's "The One" costume - Home Run Derby
Zack's "Wizard" costume - Castle Brawl