Super Mario Negaverse is about Mario navigating through a reversed universe of the Mushroom Universe, where everything is reversed. He navigates through several galaxies to open the gate to Diablo (The third Mario brother kidnapped by Bowser as an infant, trained to be evil) Palace, to rescue Peach and Luigi.
Mario is running through toad town to meet Luigi and Peach for a picnic. When he arrives on the hill, a dark ring forms around them, they hear an ominous laugh as they dissapear into the shadows. They find themselves in a series of cells, and Diablo tells them about how he created the negaverse with his dark staff he found snooping in the Palace of Shadow (Paper Mario The Thousand Year Door). He tells them about how the Negaverse is the exact opposite of the original Mushroom Universe, where all of the good guys are evil, and all of the bad guys are good. He shows them that the original universe will fade in two weeks, leaving the dark universe in its place. Mario finds a way to escape his cell, and he runs across the castle, finding that his only way out is a large cannon that will shoot him straight across the universe. He promises to Peach and Luigi he will come back for them, and shoots himself away from the castle.
World 1: The Black Forest Galaxy ClusterEdit
Mario lands on a large planet, much like the one he fought Bouldergeist on in Super Mario Galaxy. Upon looking around, Bouldergeist appears in front of him, telling Mario he is the good version, and he will not harm Mario. He tells mario that he must recover all of the pieces of the golden key to get into Diablo's Palace. Bouldergeist shows mario there are 120 peices of the key, and he will use his planet to help Mario travel throughout the universe.