Mission:Impossible
Mainland Glitch
This glitch is pretty simple to do. Enter the Turbo Code (C-up, Z, C-up, Z, C-up) and, as the title says, select the Mainland level. When you get there, run to the circuit breaker where you cut off the camera and searchlight power. Now, walk over to the end where you're facing the Gunboat. Back up a little, get positioned, and jump on. As soon as you land, try to jump to the other ledge. If you did, it will show a movie of Ethan attempting to walk in the boat and fall in the water.
Credit Goes To: Mike Gauthier(Miken64@iol7.com)

Invincibility
Put in R , Z , C-Down , R , C-Down to be invincible.
Credit Goes To: KBa6181910@aol.com
 Mainland Glitch
 Invincibility
 Giant Head Mode
 Kid Mode
 Turbo Mode
 Meet the
 Infrogrames Team
 Mini Rocket Launcher
 7.65mm Silenced
 Pistol
 9mm Pistol
 Uzi w/ 30 Rounds
Giant Head Mode
To activate giant head mode, at the level selection screen press C-Down, L, C-Up, C-Right, L. If done correctly you'll hear Ethan say "there, that's better."
Credit For Code Goes To: IGN 64

Kid Mode
At the level select screen input: C-Down, C-Up, R, L, Z. You will hear Ethan confirm. This code enables "kid" mode -- all players are small and kid-like.
Credit For Code Goes To: Jason Long via IGN 64

Turbo Mode
To get "Turbo Mode", at the level select screen input: C-Up, Z, C-Up, Z, C-Up until you hear a Horn honking and Ethan saying "Ah, That's better!"
Credit For Code Goes To: Josh Tobin & Chaz Schwartz via IGN 64

Meet the Infrogrames Team
After you complete Mission: Impossible on "possible," wait till the credits are over. You will now be able to go back into the Embassy and meet the Mission: Impossible (second) design team. Talk to all the people (until your health bar is full) -- then you will get a bonus animation of Ethan, that little devil.
Credit For Code Goes To: IGN 64

  Mini Rocket Launcher
To get the Mini Rocket Launcher press R, L, C-left, C-right, C-down at the level select screen. This will give you the mini rocket launcher and 30 rockets in levels where you can't usually get one. NOTE: If you did the code correctly Ethan will say "There, that's better."
Credit For Code Goes To: JediLynx via IGN 64

7.65 Silenced Pistol w/ 30 Rounds
At the level select screen, press: C-Up, L, C-Right, C-Left, C-Up. If you've done it correctly you'll hear Ethan say, "Ah, that's better."

High Powered 9mm Pistol w/ 30 Rounds
At the level select screen, press: R, L, C-Down, C-Up, C-Up. If you've done it correctly you'll hear Ethan say, "Ah, that's better."

Uzi w/ 30 Rounds
At the level select screen, press: C-Right, C-Left, C-Right, C-Down, R.If you've done it correctly you'll hear Ethan say, "Ah, that's better."
Credit For Above 3 Codes Goes To: Doug Harris via IGN 64