Dimentio

"And so I strike, like an unseen dodgeball in an echoing gymnasium" ~Dimentio He was one of Count Bleck's minions. He battled the heroes several times throughout the game. After Count Bleck is defeated he attempts to kill him but Nastasia takes the hit and then he seizes the Chaos Heart for himself and transforms himself and Luigi into Super Dimentio. He banishes Count Bleck, Nastasia's dead form, and Tippi to his own Dimension D. A dimension of his own creation, where anyone inside becomes 256 times more powerful than normal. Mimi and O'Chunks arrive there to tell Count Bleck they'll aways stick by him. Mario, Bowser, and Peach defeat Super Dimentio, freeing Luigi and defeating Dimentio. However, Dimentio leaves behind a shadow of his power to keep controlling the Chaos Heart. Count Bleck and Tippi and probably destroyed that shadow along with the Chaos Heart when they proclaim eternal love for each other. Dimentio was never killed. He was only sealed inside the Chaos Heart.

"Loyalty" to Count Bleck
Apparently, Dimentio approached Count Bleck on his own at first, offering to serve him. Bleck turned him down, however. It was only after reading about him in the Dark Prognosticus that he allowed Dimentio into his forces. Dimentio is seen with O'Chunks, Mimi, and of the meetings of Bleck's henchman. Even before betraying the Count, he holds disdain for all of Bleck's other followers. He takes every opportunity to mock his fellow minions over their failures, and even persuades them to disobey the Count's orders on one occasion.

Dimentio eventually learns that Bleck has a more emotional side when he eavesdrops on him and Nastasia talking. Dimentio also learns of Tippi's connection to him and uses this to weaken Bleck emotionally to make him more easy to defeat.

Dimentio is apparently "the dark one" mentioned in the Dark Prognosticus as opposed to Bleck. If Bleck read this in the Prognosticus, he might have intentionally enlisted Dimentio's help in order to ensure his successful suicide and destruction of the universe.

However, Dimentio eventually turns on Bleck, and starts trying to thwart Bleck's plans. He casually begins to help Mario along, and even tries to convince the party to join him. Bleck wants to end all worlds in order to end his own life, whereas Dimentio wants to end all worlds in order to become king of a universe of his own creation. Their difference in motive is the reason Dimentio gives for betraying Count Bleck. However, it is also possible that Dimentio only feigned allegiance to Count Bleck in order to obtain the Chaos Heart.

Encounters with Mario and Company
Mario's first encounter with Dimentio comes before fighting the Chapter 1 boss: Fracktail. Initially, Fracktail is only a security device meant to deliver the Pure Heart to the legendary Prognosticus Hero, but Dimentio appears and threatens Mario before using his magic to turn Fracktail on the plumber.

Dimentio fights Mario himself near the top of the Dotwood Tree, transporting himself and the party to Dimension D, a creation of Dimentio's meant to multiply his power by 256 times; The plan backfires when Mario's power is amplified as well, and Mario defeats Dimentio.

Dimentio later encounters the party in the Floro Sapiens' lair, where he uses a Floro Sprout to brainwash O'Chunks into a more powerful "O'Cabbage" who randomly shouts the names of vegetables.

After Bleck successfully destroys Sammer's Kingdom, Dimentio appears before a distraught Mr. L (Luigi) and supposedly "kills" him in a magical explosion. He then appears before Mario's party in Merlon's house and appears to in the same manner. Mario and his party are sent to The Underwhere, but are reunited with Luigi and able to return to Flipside.

Dimentio serves as Luigi's final boss in Castle Bleck, with hundreds of Dimentio clones appearing throughout the mirror halls in Chapter 8-3. He forces the Mario Bros. to play "tag" by chasing him through all seven areas of the game. After the Brothers catch him, Dimentio reveals his intentions to betray Bleck and asks Mario and Luigi to join him. Agreeing, however, results in a game over after Dimentio brainwashes Mario with a Floro Sprout. When the brothers refuse his offers, he insults Luigi's mustache, leading to a one on one clash between the two. When Luigi defeats Dimentio, the twisted jester acknowledges his power and pretends to blow them both up in a magical explosion, knocking Luigi unconcious to keep "the man in green" out of Bleck's "velvet-lined gloves".

Luigi survives, however (as does Dimentio), and returns to Mario just in time to face Count Bleck. After Mario and his party defeat Count Bleck, Dimentio appears and fires a lethal shot of energy at the Count in a final attempt to kill him. Nastasia jumps in the way to absorb the blast and is seemingly killed instead. Dimentio takes this opportunity to mock Mario's party before stealing the Chaos Heart and transforming Luigi into a large puppet which he took control of, creating Super Dimentio, Super Paper Mario's final boss.

"The Dark One"
In Merlon's recitings of the Light Prognosticus, he recites something along the lines of "and the dark one will use the Chaos Heart to end all worlds". While Count Bleck does attempt to accomplish this goal, and is a member of the Tribe of Darkness, Dimentio is the villain worthy of the title.

Dimentio is perhaps one of the most cunning of Mario's enemies. Residing in the shadows of Count Bleck's army, Dimentio carefully plans and executes his scheme to take control of the Chaos Heart. He plans to use its destructive power and purpose to destroy all worlds and create brand new ones to control and rule over. In Count Bleck's minionship, Dimentio waits for Bleck to create the Chaos Heart and form the void.

Dimentio is arguably the most powerful villain Mario has ever faced as well. His magical powers, dimension-hopping abilities, and near success in destroying the universe are feats not even Bowser could accomplish. Even Bowser puts aside his hatred for Mario (with a little persuasion from Peach), in order to help fight Dimentio and Bleck. While he appeared to be destroyed with the rest of Super Dimentio, the Chaos Heart and Luigi survived, so it is possible that the jester survived as well. Flopside was created as the dark version of Flipside in order to create balance, because darkness without light and light without darkness can never hope to survive. Mario was (obviously) left alive after the events of Super Paper Mario, which could mean Dimentio is still alive as well, maintaining the Dark/Light balance. Dimentio's fate has yet to be revealed.

Trivia

 * Dimentio has features of a jester, a clown, and a magician. He wears a court jester costume with clownish colors, and he has great prowess in magic tricks. Dimentio's face is also Comedy Mask, which is a classical theatrical mask used in plays.
 * Dimentio's character design resembles a stylized version of the Jesters from Super Mario RPG: Legend of the Seven Stars. He also closely resembles Harley Quin, another jester character from the game Wario's Woods, and Super Dimentio's spinning cape imitates that of Harley.
 * Mysteriously, Tippi seems to have known Dimentio before the events of Super Paper Mario. She recognizes him immediately on their first encounter in the game, during the dialog shortly before Mario battles Fracktail. However, the game never touches on this again, leaving the player to only speculate as to the meaning of it all.
 * It is implied that Dimentio has his own brand of perfume, called "Demented, by Dimentio". He offers Mario a signed bottle of it in Chapter 8-3, listing it among other bribes to persuade him to help fight Count Bleck.
 * In Flopside, if one listens to the bartender Carson's stories, there is one about Dimentio that seems to hint at him possibly being the one who wrote the Dark Prognosticus, for the fact that his role was mentioned in the book sounds suspicious. The exact text that he says reads: "So Count Bleck has four minions, as you know. I hear that one of them, Dimentio, wields powerful magic. I don't know where he comes from or who he is... But I hear he approached and befriended the count all on his own. And the count even turned him away once... Until he read in the Dark Prognosticus about the role of someone similar... Why was he mentioned in the Dark Prognosticus? Sounds fishy to me!"
 * Interestingly, the seemingly good Shaman Merloo is known to have similar abilities to Dimentio (being a powerful magician who could control dimensions); Merlumina, an ancestor of Merlon wrote the Light Prognosticus, perhaps further verifying the possibility that Dimentio, who was perhaps related to Merloo, is the Dark Prognosticus's author.
 * Dimentio is never seen walking. Just floating or standing.
 * Dimentio has been rated as the hardest Nintendo boss to fight in all Nintendo-released games.
 * There is some speculation that the Chaos Heart is actually a manifestation of Dimentio's actual heart.
 * Dimentio's "Dimension D" is able to multiply anyone's power by 256 times. That is how many web colors there are. It is unknown if this was intentional.

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