Ninja Gaiden 2: Dark Sword Chaos Cheats

On the title screen, hold up+left, select, A, and B all at once. Then press start.

Let title screen fade to black, press start, repeat, then hold up + left + select + A + B and press start.

Near the end of stage 4-2, there's a 1UP. Get it, and then go back up the ladder and out of that area. Return, and the 1UP will be there again. Repeat this process until you have as many lives as you need.