Only 3 or 4 levels in the game actually have their own passcode. Therefore, if you want to practice ILs, you would have to enter a level before it and play through it and it's just a pain.

¤ This is the only accepted method for IL practice. You must use the passcode screen to select the level for ILs.

On the title screen where the game plays the Tom and Jerry TV intro sound in glorious 8-bit, mono sound, enter this code:

Right B Up Up Left A START

You will hear an audio cue that signifies you have entered the code correctly. Press start again to move onto the selection screen and select "Password."

This level select screen should appear