Big Heads mode
Go to the main menu then hit 'my corner' and press LEFT, RIGHT, LEFT, RIGHT, LEFT, RIGHT, LEFT.
Fight as Big Tigger
Go to the main menu. Select My Corner, then Record Books, then Most Wins-Boxer. Hit up to play as Big Tigger in middleweight category.
Get all venues
Highlight My Corner at the main menu, then hit Left3, Right3, Left, Right2.
Get Ring Girls and Trucks
Finish Career mode and win fights to unlock these and many other bonuses