Gate of Thunder

Level select:
Press I, II two times, I, Select, I, II, I, II, Select two times at the title screen. A "Stage" option will now appear on the "Options" menu.

Bomberman mini-game:

Press Up, Right, Down, Left, II at the menu where you can select between the three games. A sound will confirm correct code entry before the Bomberman title screen appears.

출처 : http://www.gamewinners.com/DUO/GateOfThunder.htm