Metal Gear Solid: The Twin Snakes cheats and cheat codes for Gamecube

Control intermission view:
When the "Camera Change" or "Camera Free" message appear during an 
intermission sequence. Hold L + R to zoom or C-stick to change the view. 

Get extra Health:
During the Ninja boss fight, shoot the Mario figure on the desk

Unlock secrets:
You can be unlocked on any difficulty these secrets:

Finish the game once: Unlock Extreme Difficulty Mode
Win the game 2 times: Crimson Ninja and Sneaking Suit Meryl
Finish the game 3 times: Different ending theme
Finish the game with Meryl's ending (don't submit during torture): Meryl Demo
Finish the game with Otacon's ending (submitting into the torture): Otacon Demo
Get the Camera and Win the game: Start with Camera
Win the game as Tuxedo Snake while saving Meryl: Meryl Demo (new Costumes)
Win the game once as Tuxedo Snake while saving Otacon: Otacon Demo (new costumes)
Win the game with each ending.: Tuxedo Snake
Win the game with Meryls ending (Endure the torture): Bandana
Win the game with Otacons ending (Submit to the torture): Stealth
Win the game: Boss Survival Mode