IKARI WARRIORS

Extra continues:
To continue when you've lost all your lives, press A, B, B, A
before the Game Over appear.

Level select:
On the title screen, press Up, Down, A, A, B, Left, Right, A, B,
Up, A, Down, Right, Right, Left, B, Up, Left, A, Right, B, Left,
Right, A, Left, Up, A, Down, A, Right, Left and finally B very 
quickly. Use A and B