Double Dragon (Arcade)

A billboard advertising Nekketsu Kouha Kunio-kun (the Japanese version of Renegade) can be seen atop the building in Mission 1 just before the boss battle. However, the vertical scrolling stops after a certain point, making only the lower portion of the billboard (just below Kunio's eyes) visible.

The standing knee kick is another unused technique for the Lee brothers that was later implemented in Double Dragon II.

Animation frames of Zack (aka Abobo) performing the two-handed-slap technique. In the actual game, this move is used exclusively by Jack, his mohawked head-swap variant who serves as the end-boss of Mission 1 and Mission 3.

Jeff, the Mission 2 boss, is likewise a head swap of the Lee brothers themselves. He has a full set of sprites performing almost every possible action that can be carried out by the player, despite the fact that he lacks the ability pick up or use any weapon either, making every sprite where he is swinging, throwing or kicking down something unused. In Double Dragon II he gained the ability to wield grenades, putting his throwing animation to use in that game.

08

A somewhat sad-sounding jingle that lasts only eight seconds. Perhaps it was meant as a Game Over theme since there isn't one in-game.

0E

The music heard during the stage transitions after the boss battles is normally cut off before the whole track can be played. It is possible to softlock the game on the post-Stage 1 transition, making it possible for the whole track to play. Two known instances of this being used in full is the first part of Mission 4 in the Game Boy game and in Double Dragon IV during cutscenes and the character selection in Duel mode.