Mysterious Dimension

The Mysterious Dimension (, Mysterious Space) is a sub-world found in The Dark Realm within Adventure Mode in Super Smash Bros. Ultimate. It is located at the end of the north path, and the boss of this sub-world is Marx. Uniquely, this sub-world appears to be based on various locations in the real world, as well as locations in games, rather than being based on a specific area in a fictional universe. Objects such as torn up roads, large, green pipes from the Mario universe, blossoming cherry trees, a Coliseum from the Fire Emblem universe (or the Roman Colosseum), street lights, a pirate ship, and what is evidently a black hole can all be seen. The sub-world appears to have a theme of chaos, destruction, and disarray, a theme fitting the mischievous Marx. The dimension appears to become more decayed and chaotic the closer the player gets to Marx, culminating in a swirling vortex.

Spirits
The spirits found here do not follow any particular theme, though some are grouped by universe. Instead, they are found by answering trivia questions about the various game series featured in Ultimate; fighting the spirit that corresponds to the correct answer opens the path forward while answering the question correctly the first time will award the player with a chest containing extra snacks or Spirit Points. The only punishment for an incorrect answer is having to guess again and not having the chest appear.

Trivia answers
The answers listed in bold are correct; the question about which spirit Kirby cannot inhale has two correct answers.

Boss
The boss of this sub-world is Marx. In order to reveal his location, the player must defeat the Tabuu spirit.

Captured Fighters
All fighters are accessed normally in this sub-world. The player must defeat Greninja, Ike, and Meta Knight in order to progress.

Chests
Eleven chests can be found in this sub-world. The chest will appear after answering the trivia quiz correctly unless already answered incorrectly.

Trivia

 * The Mysterious Dimension has the most captured fighters of all the sub-worlds, with a total of nine.
 * The Mysterious Dimension is the only sub-world in the Dark Realm not to contain any captured echo fighters.
 * It is also the only sub-area in the Dark Realm to contain neither (sole) female nor third-party fighters.
 * It is also the only sub-area to contain at least one character introduced in each installment.
 * By extension, this is the only area in the Dark Realm to feature a fighter from the original Super Smash Bros. game, being.
 * The Mysterious Dimension is the only sub-world in the Dark Realm where all of its fighter battles are accessed normally.
 * Mysterious Dimension and Base are the only sub-areas to have an original soundtrack.
 * Additionally, it is the only sub-area in the Dark Realm that does not change its soundtrack.