To get all the characters you have to beat the game with all the players you first start with. Ball mode and Theater mode- Beat the game will all players you start with.
To get Gon you must beat him in the ball mode.
To get Dr. B you have to beat the force mode FOUR times.
To get Anna Williams you have to beat the arcade mode with 5 different characters.
To get the hidden costumes for:
Anna- Choose her at least 25 times
Gun Jack- Choose him at least 10 times
Jin-Choose him at least 50 times
Xiaoyu- Choose her at least 50 times
Forest Law- Selectable from the beginning of the game.
Tiger- Goto Eddy and select him by pressing Start. You ahould have completed the Arcade mode with 16 differend characters. Tiger has the same moves as Eddy but a different ending. He is the last puzzle in getting all the endings.