At the title/select screen 

Hit select ten times, then play a game, the fighters will be "deform." You will hear a bing if it is done right.

Press Right ten times, then the fighters will be "paper thin." Bing you did it right.

Hit Left ten times, then the fighters will be "stick." Till you hear a bing.

When your at Player's Select

Hold down, X+O, then the fighters will be "small Fighters."

Hold Square+O, then the fighters will be in "new outfit."

Beat the game 4 times, then you get 4 new fighters