Jack

Jacks are rotating obstacles in Zelda's Adventure, resembling four red spheres orbiting a white one. In both appearance and function, they are strikingly similar to Bubbles, particularly the incarnation in The Legend of Zelda: A Link to the Past, though they lack the skull design. They appear solely in the Shrine of Destiny, where they bounce around rooms diagonally. Unlike Bubbles, they are capable of reversing their direction when hitting a wall instead of always bouncing at 90 degrees. They are completely invincible, though they present less of a threat than the Gibdos they are found alongside due to dealing less damage. In one room, a Jack spawns every time a Gibdo is defeated, and in another, a Crystal Switch causes two to appear.