Sound test:
Hold L + R on controller two when the Nintendo logo appears.
Special Circuit:
Complete the Major, Minor, and World circuits without losing a match.
Japanese text:
Have at least one empty save file slot available. Highlight the "New Game" option on the main menu and press A + X.
Character sequence:
Defeat the game without losing once to see a small scene for each character as they appear.
Health recovery:
Rapidly tap all buttons while your opponent is on the floor to quickly regain health.
Defeating Mad Clown:t[
Pause game play immediately before Mad Clown throws the balls at your boxer. This will allow you to see which way you have to move to avoid them.
Defeating Nick Bruiser:
Nick Bruiser moves fast for the first few punches if he punches at your face -- you can only hit him in the face for the first three hits. If he does a Torso Punch, hit him in the lower torso one time in the torso and two times in the face. Note that he moves around like Hoy Quarlow when you punch him. When he moves up to the center and jumps down at you, just dodge to the right and duck because he is going to punch you twice. You can super punch him in the torso if he does not block, but if he tries to slam his fist like Rick Bruiser, dodge and super punch him. When he sounds like a bull, block the torso, then the face until he does an uppercut. Dodge that and punch him, then super punch him. Repeat this until he is defeated.