JJ (ジェイ ジェイ Jei Jei?) is an action game developed and published by Square for the Famicom in 1987. In English, it is sometimes referred to by its long form, Jumpin' Jack, or by its subtitle, Tobidase Daisakusen Part II. The game was only released in Japan.
The sequel to Tobidase Daisakusen (known in North America as 3-D WorldRunner), JJ is a typical scrolling shooter, but it incorporates a third-person view, where the camera angle is positioned behind the main character. As in the previous title, the main character Jack must travel through various worlds, armed with his laser cannon and jumping ability, to defeat the serpentbeasts who have overrun the planets.
JJ was the last game by Square to utilize the "3D mode" and 3D glasses, and was Square's last work before the inception of the popular Final Fantasy franchise. The soundtrack of JJ consists of eight tracks, and all of them are either remixed or reused from the game's prequel, 3-D WorldRunner. The game was scored by Nobuo Uematsu, and is Uematsu's 16th work of video game music composition.