Metal Gear Solid: The Twin Snakes Cheats

Look on one of the file cabinets in Otacon's office to find statues of Mario and Yoshi. Shoot the Mario statue to hear the classic "extra life" sound, and increase your health. Shooting the Yoshi statue does not do anything except make a sound.

Unlock Bandana and Unlimited Ammo:
With Meryl's ending complete the game once.
Unlock Boss Survival:
With either ending complete the game once.
Unlock Stealth Camouflage:
With Otacon's ending complete the game once.

After you beat the Tank, and go into the Nuclear Storage Facility, go up the ramp to your left. At the top of the ramp, take a photo of the glass infront of you. Don't zoom in after you get to the top of the ramp, just take a pic. When you look at the photo later on in the Photo Viewe, it will contain a ghost, holding a knife, wearing a spiffy Gumbi shirt.

Successfully complete the game three times to hear alternate music during the ending sequence.

After your battle with Ninja, take a time to look around Otacon's office. You'll see a Yoshi and Mario statue on a filing cabinet. Shoot the Yoshi and he will make his classic noise. Shoot Mario and a 1Up will appear above his head. In addition, you will get a health bonus with each 1Up.