Tasks, aids, and obstacles[edit]
In each world, the player is free to travel in any forward-moving direction. The worlds are filled with enemies that attack Jack or block his progress, but also contain items that are either helpful or deadly to Jack; most of these items can be found in columns spread throughout each world. Canyons, which Jack must leap over, are also present in each world, and at the end of each world is a boss the player must defeat. None of the elements, items, or enemies in JJ are randomized; instead, they are defined in set locations.
All of the elements listed below appear in every world (the stopwatch, coils, and super-coils excepted), but not necessarily in every level:
- Canyons
- Canyons are present in each world, although the width and number of canyons differs greatly.
- Bosses
- Bosses appear at the end of every level and must be defeated to advance. The number of incarnations of a given boss increases from world to world. In World 1, for example, the player must defeat one boss, but by the eighth and final world, the player must face no less than six incarnations of the same boss.
- Enemies
- Each world has different enemies, but three types are consistent throughout each world: eyeballs, fireballs, and fire pillars. World 2 introduces the indestructible cell cluster, a new type of enemy that doesn't hurt Jack, but attempts to block his progress by shadowing his movements. As the player advances, the enemies of each world are progressively more difficult.
- Columns
- Columns litter every world, and are important as they house items that benefit Jack's progress (with the exception of the eye, which is lethal). Items in columns are obtained by crashing into them.
- Coils
- Coils first appear in World 3. When stepped on, coils send Jack high into the air, and are essential for crossing some canyons.
- Super coils
- Super coils are flattened in appearance, and serve the same purpose as coils, except they send Jack even higher into the air.
Worlds[edit]
In JJ there are eight worlds composed of two to four levels each. Every level acts as a checkpoint; if Jack dies in World 1, level 3, for example, he continues at the beginning of World 1-3. Completion of each level also resets the time counter. Additionally, each world has a bonus level, denoted as level B.
- World 1 has four levels.
- World 2 has three levels; there are two incarnations of the boss at the end of World 2. World 2 also marks the first appearance of cell clusters.
- World 3 has four levels, and is unique because it marks the first appearance of coils. Like in World 2, there are two incarnations of the boss.
- World 4 has four levels, and it introduces super coils. At the end of World 4 are three incarnations of the boss to fight.
- World 5 has three levels. Meteorites in this world pose as cell clusters, but the meteorites are actually harmful. There are four incarnations of the boss.
- World 6 has four levels. Like in the previous world, there are four incarnations of the boss.
- World 7 has three levels. Like in the previous world, there are four incarnations of the boss.
- World 8 has two levels. It's vital that the player acquires the stopwatch in this stage. The player must face six incarnations of the boss, and the boss blends in with the background.