Complete the World League at level 4 or higher. Then when playing against the World Stars, press Up, C-Up, Up, C-Up, Down, C-Down, Down, C-Down, Left, C-Left, Right, C-Right, Left, C-Left, Right, C-Right, B, A, Z + Start.
Big head mode
At the title screen, press C-Down(2), C-Up(2), C-Right, C-Left, C-Right, C-Left, B, A, Z + Start. If you entered the code correctly, you will hear a sound.