Alternate-dimension Mobius is a dimension that is an alternate reality version of the planet Mobius as a seemingly dark, false utopia, and a location in the episode "Six is a Crowd" of Sonic Underground. This dimension was created by the Oracle of Delphius to show the Sonic Underground what happens when power corrupts. It is where the Royal 'Corrupt' Hedgehogs rule with an iron fist, and where Good Robotnik resides.
Not much is known about this place, but what is seen appears to be a version of Mobotropolis made in the image of the 3 hedgehogs. In one area of town is the Royal Palace, an enormous palace (clearly unlike the one in the episode "Wedding Bell Blues") with a golden front gate with designs resembling hedgehog quills. SWATbots patrol every section of the city and serve as guards to the royals, and the citizens live in abject poverty due to their own rulers' cruel and selfish acts.
After their battle with their cruel alternate counterparts, Sonic along with Manic and Sonia, decided to show the three the error of the ways (though they had no way to take them to Robotropolis in the heroes' original universe). Good Robotnik took them all on a "grand tour" via his Freedom Fighters' chili dog mobile throughout Mobotropolis including a street district that used to be teeming with thriving family-owned businesses. He then took them to a secret location in a forest outside Mobotropolis where there is music and freedom. At the music auditorium in the forest, the 3 hedgehogs renounced their harsh ways and gave back all the money, beauty, and freedom to all the people of their kingdom and harmony was restored to the alternate Mobius before the Sonic Underground used the power of their amulets and returned home to their reality.