MLB SlugFest - Loaded:
Fantasy Stadiums and Teams: 
At the main menu hold Triangle + Square + R1.

Codes are entered at the VS Screen:

Big Head Mode: 
Right, Square, Square. 

Extra Time After Play:
Left, Square, Triangle, Triangle, Circle, Circle, Circle. 

Max Batting: 
Left, Square, Square, Square. 

Max Power: 
Left, Triangle, Triangle, Triangle. 

Max Speed: 
Left, Circle, Circle, Circle. 

Rubber Ball Mode:
Up, Square, Square, Triangle, Triangle, Triangle, Triangle, 
Circle, Circle. 

Softball Mode:
Down, Square, Square, Triangle, Triangle,Triangle, 
Triangle,Circle, Circle. 

Tiny Head Mode:
Left, Square, Square. 

Unlimited Turbo:
Down,Square,Square,Square,Square,Triangle,Triangle,Triangle,
Triangle,Circle,Circle,Circle,Circle.