Rocky Cheats

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.

Double Damage Mode
Hold R and press the following combination at the Main menu:
Right, Down, Left, Up, Left, L.
Double Speed Mode
Hold R and press the following combination at the Main menu:
Down, Left, Down, Up, Right, L.
Max Stats (Movie)
Hold R and press the following combination at the Main menu:
Right, Down, Down, Up, Left, L.
Max Stats (Tournament & Exhibition)
Hold R and press the following combination at the Main menu:
Left, Up, Up, Down, Right, L.

Enter the following code at the main menu: HOLD R and then press up, down, down, left, left L

Successfully complete movie mode under the Champ difficulty setting.

Complete Movie Mode on the Contender setting.
Source: IGN.com