Superman
Level Skip
At the main menu, press C-Up, C-Down, C-Left, C-Right(2 times). Start a new game, then press Start, C-Up, C-Down during the game.

Heat Vision
In the Lexcorp, destroy all the dark shadows. After they are gone, look behind the short stone wall with the red velvet ropes attached for heat vision. Pick it up and start setting some trees on fire.
 Level Skip
 Heat Vision
 Fall-Through Floor
 Infinite Abilities
 Level Select
 Beating Darksied
 Become a Car
 Stop the Bombs
Fall-Through Floor
In Practice mode, FLY through all the rings around the Lex-Corp building until you get to the red ring. LAND and WALK through it. The floor will fall in and you will be under Virtual Metropolis in water! You can't move, but the view is neat. Plus, you're under water. The only way out is to restart the mission or quit.
Credit Goes To:Jacob Norris via N64cc

Infinite Laser Vision, X-Ray Vision, Freeze Breath, and Running Boost
At the title screen, hold A + B + C-Up + C-Down and press Start

Level Select
Begin a game in single player mode. Play until getting the option to save the game on the controller pak. Save the game, then reset. Select the load game option from the main menu, then choose the game that was saved. A prompt to insert a rumble pak will appear. Hold L + B for one second, then press A. A level selection screen will appear that allows any mission to be played on the current difficulty setting. Note: The difficulty setting may be changed by entering the option screen from the main menu.
Credit Goes To:Cheat Code Central

Beating Darksied
Play through the eighth level until you get to the bomb in the kryptonite room. Freeze it with your freezing breath and when you walk out Jimmy Olsen should be waiting for you. Talk to him then when he leaves go out through the path where the kryptonite room is. Go all the way around. When you get back in the same place you should see Darkseid waiting for you. Stand behind him (at a safe distance) and toast him with your heat vision. He should just stand there as you kill him. Pick him up and take him to the cops at the beginning of the level.

Become a Car
To become a car, first go to practice in the title screen, then while in the practice mode choose if you would like to kill the enemy shooting at you or not it doesn't matter, then pick up the car (with B) and fly with it (Z) then go through all the rings around the Lexcorp building and once you fly through the last red ring (remember you MUST fly through it, if you walk through it the trick won't work) the game should glitch, and you should end up in the car! Now you can go around Metropilis in style!
Credit Goes To: Allan Pries via IGN 64

Stop the Bombs
To stop the bombs at the dam and the Daily Planet, use your freeze breath. Make sure they're frozen solid.
Credit Goes To: Wexpac via IGN 64