Double Dragon (NES)/Secrets

Infinite experience points
If you would like to level up your fighter to the maximum level without a lot of hassle, there are two opportunities to do so in the second mission. The first time is during the section with several Williams where you must climb the fence to cross the gap in the floor. After you drop down to the other side, two Williams will approach from the right. Wait until the higher Williams has walked past the red steel girders in the background. Then climb the fence and walk as far back to the left as you can. Return to the location where the Williams last stood, and attack the space he previously occupied. You will get credit for striking an invisible opponent and earn points towards higher levels of experience. You can do this for as long as you like, until you reach the seventh and final level, but you do risk running out of time in the process.

The second location where this trick is possible is the section after where you must fight several Lindas as you climb the scaffolding. Allow two Lindas to appear on the bottom level, and then begin climbing the building as high as you can. Other Lindas may appear to attack you, but you can climb back down and attack the location where a Linda once stood on the bottom level and earn experience points while you attack the empty space where she used to be.

Skip the Mission 2 boss
In a similar manner to the trick described above, it is possible to bypass the fight against the first Chintai at the top of the building in Mission 2. Climb all the way to the top and make the Chintai appear. Then simply climb back down to the bottom of the building. Eventually the Chintai will scroll off the top of the screen, and the game will consider Chintai defeated, triggering the end of the mission, and allowing you to proceed to the next level of the game.

Odd weapons
The game does not allow you to transfer weapons from one section of the game to the next. Weapons typically disappear after the thumbs-up symbol alerts you to the chance to proceed. However, if you successfully collect a weapon from the floor by the time the thumbs-up finishes flashing, the weapon will appear as a garbled bunch of pixels. Normally this will not help you very much. However, it is possible to use this trick to your advantage at the very end of the fourth mission. After defeating two Abobos, two Chintais will appear and one will be holding a knife. If you manage to collect the knife right when the last Chintai flashes for the fourth time, you will be holding something in your hands which you can swing like a bat. You risk losing the weapon every time a new enemy is set to appear unless you allow yourself to be attacked, dropping the weapon, and collect it once more when the last enemy flashes four times. If successfully performed every time, you can continue to utilize a weapon all the way up to the fight against Jimmy.