In the NES version of Double Dragon, you have this weird Heart System to deal with that earns your moves. Essentially, as you beat up bad guys you get heart points, get 1000 heart points and you get another heart and another fighting move.

It's kind of tedious to earn moves this way, I'd much rather have all my moves up front for maximum face-smashing potential.

So, to speed the process along, go to Mission 2, right past the big pit. Go just far enough to make the two Williams appear. Let the top one get to about the end of the girders in the background and then hop back on the fence, they'll freeze in place.

Go all the way back to the left as far as you can. You don't have to fall off the ledge like I did here, but I think Billy's face is pretty funny if you do.

Then go back to where the upper William was and start attacking. You'll hit him over and over again, even though he's not there.

Keep going until you have 7 hearts, the maximum.

Then you'll have your entire martial arts toolbox available to use.

Good luck!