Ninja Raiden:

Beat 50% of Raiden's VR missions.

Raiden X:

Beat 100% of Raiden's and Ninja Raiden's VR missions.

Pliskin:

Beat 50% of Snake's VR missions.

Tuxedo Snake:

Beat 100% of Pliskin's VR missions.

Metal Gear Solid 1 Snake:

Beat 100% of Pliskin, Snake, Tuxedo Snake, Ninja Raiden, Raiden X, and Raiden.

Photograph mode:

Beat Bomb Disposal, Eliminate, and Hold-Up modes.

Sunglasses:

Beat the game twice and Snake and Raiden will be wearing sunglasses.

European Extreme difficulty:

Beat the game under normal difficulty.

Boss Survival mode and Casting Theater:

Beat Sons Of Liberty under any difficulty setting.

Control Title Screen:

Press White to hear a gunshot and use the Right thumbstick to change the colors.