Press Triangle + Circle to do a boxer's signature move. For example, press Triangle + Circle with Tua and he will do his devastating left hook.
Box as The Bulldog
Enter "BULLDOG" as a name in career mode to unlock The Bulldog.
Box as Ashy Knucks
Enter "KNUCKS" as a name in career mode to unlock Ashy Knucks.
Box as a Bear
At the main menu, press Right + Square, Right + Triangle, Right + Circle, Right + X. If you entered the code correctly, you will hear a sound. Then select any boxer to play as a bear.
Big Head Mode
At the main menu, press Left + Circle, Left + Triangle, Left + Square, Left + X. If you entered the code correctly, you will hear a sound.
Select career mode, create a boxer, and enter "PSIRULES" as the name. Save the created boxer and exit career mode. Then, enter career mode again and load the boxer, which will now have full attributes and other special features.
When given a choice to hit the heavy or speed bag between fights, hold L1 + L2 + R1 + R2 to regain two to eight points of energy, depending on how long the buttons are held.
During a match, press R1 + R2 + X.