WorldRunner features many sprite-based elements that are typical of a forward-scrolling rail shooter game, where the player focuses on destroying or dodging onscreen enemies against a scrolling background.

[4] As Jack, players make their way through eight worlds, battling hostile alien creatures such as blob monsters and leaping over bottomless canyons.

In each quadrant, the player can find pillar-like columns that house power-ups, objects that are beneficial or add extra abilities to the game character such as temporary invincibility or laser missiles.

[10] Players assume the role of Jack the WorldRunner, a wild "space cowboy" on a mission to save various planets overrun by serpentine beasts.

[6] In a 1999 interview with NextGeneration magazine, Sakaguchi admitted that he "liked Space Harrier", but said that his main reason for the development of the game was that Square owner Masafumi Miyamoto wanted to demonstrate Nasir Gebelli's 3D programming techniques for which he had been hired.

JJ was one of the few games to utilize the Famicom 3D System,[18] and was Square's last work before the inception of the popular Final Fantasy franchise.

JJ is a sort of "dark version" of the original game; it moves at a much faster pace with increased difficulty, plus a more "sinister" art style and use of color.