Secret Levels.
At the game mode screen, press Up to enter a Secret Mode screen which should be empty. At this screen enter the following for the follow levels
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 unlocked secret levels can be saved to memory card for future access.