Super Dimentio was born shortly after Dimentio assumed control of the Chaos Heart, which he obtained following the defeat of Count Bleck. It was stated in the Dark Prognosticus that Luigi is the ideal host for the Chaos Heart's power, so before the final battle, Dimentio placed the seed of a mind-controlling Floro Sprout in Luigi's head, and activates it when he seizes the Chaos Heart, causing Luigi to revert back into Mr. L and combine with the Chaos Heart. Dimentio then enters the monstrous puppet through its mouth, adding his power to the mix and creating the fully-realized Super Dimentio.
Super Dimentio harvested the power of the Chaos Heart, rendering him impervious to any of Mario's, Princess Peach's or Bowser's attacks and thus putting into motion the destruction of all worlds. This is similar to the final bosses of two previous Paper Mario games: Both Bowser and the Shadow Queen's final form were initially invincible when faced in Paper Mario and Paper Mario: The Thousand-Year Door, respectively. Earlier in Super Paper Mario, Bleck also started off the battle as being untouchable.
While the three heroes tried to fight it, in Dimension D, where Dimentio had imprisoned Count Bleck, Tippi and Nastasia, Bleck and his minions expressed feelings of hope and love, restoring the Pure Hearts. The Pure Hearts were then used upon Super Dimentio to weaken the power of the Chaos Heart, nullifying his invincibility and starting the real final battle. Unfortunately, before this, Flopside, Yold Town, and the Land of the Cragnons were engulfed by The Void. Super Dimentio had many attacks, including smashing his hexagonal appendages on the ground, activating a homing blast, and doing a Super Jump and smashing onto the ground. Super Dimentio was finally defeated in a magnificent explosion, releasing Luigi and the Chaos Heart from control, and leaving Dimentio dying. However, Dimentio leaves one last portion of his power behind to control the Chaos Heart and ensure that all of existence will die with him, and explodes, still smiling.