Jirai-Kun

When the enemy's turn begins (after the player's turn is over), hold Select & Start and rapidly press the A button. If done right, you should get to control the 3rd or/and 4th enemy.

While playing, lose the game and at the screen with the blinking "Press Start" (right after the cheering enemies animation), hold B and press Select.

While playing, open the map and hold Up + B on controller 2 to see where the mine is.

At the game menu, keep picking the first option until you are prompted to enter your name. Enter the following Japanese characters: Up 2 times, Right 4 times and enter the Japanese character. Up 2 times and enter the Japanese character. Up 2 times, Left 2 times and enter the Japanese character. Right 4 times, Down 1 time and enter the Japanese character. Left 5 times, Up 2 times and enter the Japanese character. Now hit "End" and the soundtest will appear.

At the game menu, keep picking the first option until you are prompted to change the disk. Hold Right + A on controller 2 and keep holding while you change the disk. When the game starts, it will play by itself.