|Part of:||File Island ⇒ Infinity Mountain|
The Back Dimension are the leftover traces of Mugendramon once it is defeated at Infinity Mountain, and can take the place of either Ice Sanctuary, Dark Lord Mansion, or Ogre Fortress at one time. Each Back Dimension consists of three levels, and its appearance is very similar to that of the interior of Infinity Mountain. Once someone reaches the final level, one will find that the location is no longer Back Dimension, but the original location.
Once Mugendramon is defeated at Infinity Mountain, Mugendramon is thought to be out of existence. Yet, if one subsequently tries to enter Ice Sanctuary, Dark Lord Mansion, or Ogre Fortress, one of these places may be taken over by the Back Dimension. If one can journey through the floors of the dimension, one would find oneself no longer in the Back Dimension, but in the original location one entered. Mugendramon will then appear in the location, alongside Analogman, and will engage in battle to those who cleared the Back Dimension.