Duke Classic Costume
Duke, real name Conrad Hauser, serves as G.I. Joe's second in command and takes the lead on most missions. Inserting a special code on the main menu screen will unlock Duke's classic costume from the 1980s cartoon series. For the Wii, press "Left," "Up," "Minus" button, "Up," "Right" and then the "Plus" button. On the Xbox 360, press "Left," "Up," "X," "Up," "Right" and then "Y." The PS3 code is "Left," "Up," "Square," "Up," "Right" and then "Triangle." For the PSP, input "Left," "Up," "Square," "Up," "Right" and then "Triangle." If entered correctly, you'll hear "Yo Joe!"
Scarlett Classic Costume
Players may also unlock the classic costume for Shana "Scarlett" O'Hara, G.I. Joe's premier female soldier, from the main menu screen. On the Wii, enter "Right," "Up," "Down," "Down" and the "Plus" button. For the Xbox 360, press "Right," "Up," "Down," "Down" and "Y." The PS3 code is "Right," "Up," "Down," "Down" and "Triangle." On the PSP, press "Right," "Up," "Down," "Down" and "Triangle."
Unlockable Characters
After successfully completing the game, you'll be able to play special Cobra levels that, once beaten, will unlock Cobra villains Destro, Baroness and Firefly as playable characters. However, each character costs 15 battle points, so make sure you have enough points stockpiled to purchase them. You can even gain Storm Shadow, Cobra's lethal ninja, as a playable character if you find and defeat him on the "Arctic," "Desert" and "Jungle" stages.
Special Achievements
Defeating enemies and accomplishing game tasks will earn you valuable battle points, but you can earn extra battle points by completing five secret tasks. Purchasing all the unlockable Cobra characters wins you 25 points. Completing any mission using Snake Eyes and Storm Shadow earns 10 points. Completing any mission using Baroness and Duke earns 10 points. Complete any "Arctic," "Jungle" or "Desert" stage using a Cobra character earns 10 points. Finally, completing all side missions will earn another 10 points.