Alternate Costumes 
     Go  to the Setup screen, then the Cheats menu. Press START, A, Z,
Y, X, START to enable the cheat.

Invincibility 
     Go  to  the  Setup  screen,  then Cheat Codes. Enter this code to
activate the cheat: START, A, A, Y, Y, Z, Z, X, X, START.
 
Tons of Power-ups 
     To  have  a constant stream of power-ups, go to the Cheats screen
of the Setup menu and press START, A, Y, A, Y, A, Y, X, X, X, START.

Unlock All Boxers 
     Go  to  the  Setup  screen,  then Cheat Codes. Enter this code to
activate the cheat: START, A, Y, X, X, Z, Z, X, Y, A, START.
 
Unlock Intercontinental Tourney 
     Go  to  the  Setup  screen,  then Cheat Codes. Enter this code to
activate the cheat: START, A, A, A, Y, Y, Y, X, X, X, START.
 
Unlock Life Mode For Everyone 
     To  unlock Life mode for all of the boxers, go to the Cheats menu
in the Setup menu and press START, A, X, Y, Z, A, X, Y, Z, START.

Unlock Scrap Yard 
     To  unlock  the  Scrap Yard, go to the Cheats screen of the Setup
menu and press: START, Y, Z, Y, Z, A, A, START.