At the game mode selection screen, press UP to enter a Secret Mode screen that should be empty. Do these footsteps to get the secret modes in this order....

Another: Up, Up, Down, Down, Up, Up, Down, Down

Maniac: Left, Left, Right, Right, Left, Left, Right, Right

Double Another & Maniac: Up, Up, Down, Down, Left, Right, Left, Right

Mirror Another & Maniac: Left, Right, Left, Right, Left, Right, Left, Right

The secret modes will then be saved to your memory card so you don't have to do them again.

Enter this code at the title screen. Select your mode (Arcade or Append, each has its own secret characters). Then hold LEFT then press START for one set of characters. Or hold RIGHT and press START for the other set. Both Player 1 and Player 2 get new characters so thats 8 characters total!