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.
At the main menu, press C-Up, C-Down, C-Left, C-Right. If you entered the code correctly, Clark will say "This looks like a job for Superman." Then, enter one of the following codes while the game is paused:
Pause the game and press C-Up, C-Down.
Pause the game and press Z, R.
Pause the game and press R, Z.
Pause the game and press L, Z.
Pause the game and press Z, L.
Pause the game and press R, L.
To end up in 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!
At the title screen, hold A + B + C-Up + C-Down and press Start for Infinite Laser Vision, X-Ray Vision, Freeze Breath, and Running Boosts.
Two controllers are required for this trick.
For Multi-Player Levels with one player, begin a new game, and set the multi-player fight options to two players, solo, town, and 5 minutes. Then, select a character and start the game in multi-player mode. Quit to the main menu, then press B. The "New Game" option should be highlighted. Press A, select one player and press L, B, A when prompted to insert a rumble pak. After a brief pause, the game will begin in the town.
To stop the bombs at the dam and the Daily Planet, use your freeze breath. Make sure they're frozen solid.