Double punch damage:
Hold R and press Right, Down, Left, Up, Left, L at the main menu.

Double speed boxing:
Hold R and press Down, Left, Down, Up, Right, L at the main menu.

All default boxers and arenas:
Hold R and press Right, Down, Up, Left, Up, L at the main menu. Note: This does not unlock Mickey or the Rocky Statue.

All default boxers, arenas, and Rocky Statue:
Hold R and press Right(3), Left, Right, L at the main menu.

All default boxers, arenas, Rocky Statue, and Mickey:
Hold R and press Up, Down(2), Left(2), L at the main menu.

Full stats in tournament and exhibition modes:
Hold R and press Left, Up(2), Down, Right, L at the main menu.

Full stats in movie mode:
Hold R and press Right, Down(2), Up, Left, L at the main menu.

Silver class knockout tournament:
Win the bronze class knockout tournament.

Gold class knockout tournament:
Win the silver class knockout tournament.

Fight as Mickey Goldmill:
Successfully complete movie mode under the Champ difficulty setting.

Rocky Statue:
Successfully complete movie mode under the Contender difficulty setting.

Hint: Easy knock downs:
In movie or any other mode, when the fighter approaches you at the start of the fight, hit him with your special power punch. When he comes to you again, hit him with another special power punch, then attack him with body shots. This will drop his strength and let you knock him down repeatedly, thus winning the fight.