Fight as Geese and the Shadow/EX characters:
Enter the ranking screen at the high score table. Quickly press Left, Down/Left, Down, Down/Right, Right, Up/Right, Up, Up/Left, Left, then hold Up/Left and press A, B, C. Geese will say "Come on" to confirm correct code entry.

Fight as Shadow/EX fighter:
Enter the character selection screen. Highlight Andy, Billy, Tung, or Mary, hold Start, and press B(2), C(2). While continuing to hold Start, hold B, pause one second, and hold C. While continuing to hold Start + B + C, press A or D to select the Shadow version of the character. Pressing A or D will select a different color.