Striker Pro 2000
To make the players look like bird people, press Up, Triangle, Left, Square, Right, O, X, X at the cheat screen while the game is paused.
Press Left, Up, Left, Up, Left, Up, Left, X at the cheat screen to unlock some new features.
Unlock Extra Stadiums:
Press Left, Left, Up, O, O, Triangle at the main menu to access extra stadiums.
Thanks to Revolution reader Jason Sommerfeld!