DOUBLE DRAGON ][

Extra lives:
If you are playing alone, select the two-player game B mode and beat
up the other character. Each time you kill the other character, you
will be rewarded with an extra life.

Continue mode:
Press the following combination to continue the game at the end of 
the relevant stage (use the 2nd. controller for entering the last 
cheat)
Up,Right,Down,Left,A       = Stages 1 to 3
Up,Down,Left,Right,B,A,A   = Stages 4 to 6
A,A,B,B,Down,Up,Right,Left = Stages 7 to 9

In stage 4, when the helicopter door opens, press the Pause button
and wait a few seconds. When you unpause the game, the door will
close.