Double Dragon (ダブルドラゴン) is a side-scrolling beat-'em-up by Technos, originally released as an arcade game in 1987 as a spiritual sequel to the 1986 release of Nekketsu Kouha Kunio-kun (known in its Westernised form as Renegade).
The game was ported twice to Sega consoles: the first version was produced for the Sega Master System in 1988 by Sega themselves (although the actual development was outsourced to Arc System Works); the second version was for the Sega Mega Drive in 1992, produced by Accolade and published under their Ballistic Software imprint, it was released without a license from Sega.
Double Dragon centers around Billy and Jimmy Lee, twin martial arts masters who must rescue a young woman named Marian from the clutches of the Black Warriors, a ruthless street gang led by the notorious machine gun-toting Willy Mackey. The game can be played alone as Billy (who wears blue), or with a partner who takes control of Jimmy (in red). Using their martial arts techniques, or whatever weapons they may arm themselves with, the Lee brothers must fight their way through a slum, an abandoned factory, and the wooded outskirts of the city, before reaching the hideout of the gang, where Willy awaits them.
The Master System version is a downscaled adaptation of the arcade game similar to the NES version released before it. While the character designs are pretty similar to the NES version, the Master System version retains the 2-player co-op mode and features level designs much closer to the arcade game (albeit, without the vertical scrolling and climbable ladders/fences in some areas). Because the arcade version used a three button setup (with a dedicated jump button), the input method of certain moves such as the flying jump kick, backward spin kick and elbow strike were changed to better accommodate the Master System's two button controls. The consecutive attacks (the uppercut and roundhouse kick) and the hair grab are also performed a bit differently. The Master System only displays up to three enemies and a single weapon on-screen at once.
In contrast, the Mega Drive version is a relatively straight port of the arcade with slight differences in graphics and sound. Most notably the backgrounds graphics are different, some of the character sprites (specifically Marian and Linda) are not 100% accurate and the head-swapped boss characters (the mohawked version of Abobo at the end of Missions 1 and 3, and the Lee brother lookalike at the end of Mission 2) are replaced with plain palette swaps.