Metal Gear Solid: The Twin Snakes 
  
Gamecube
  


Extreme difficulty:


Beat the game on Normal. 
Camera:


Beat the game once to unlock the camera. You can use the camera to snap shots
during the game, some of which give you extra surprises. 
Meryl demo mode:


Beat the game but do not submit to the torture. 
Bandanna:


  Beat the game but do not submit
  to the torture. At the end, Meryl will give you the
bandanna, which gives you unlimited ammo.
Meryl outfit:


Beat the game twice and do not submit to the torture either
time. 
Otacon demo mode:


Beat the game but do  submit to the torture. 
Otacon outfit:


Beat the game twice and do  submit to the torture both 
times.
 Stealth and Tuxedo outfit:


Beat the game twice.
Different  ending music:


  Beat the game three times.


Thanks to Revolution readers Solidus and MGS Stud!