Dimentio is one of Count Bleck's minions. He is a jester who is the master of dimensions, but is perhaps one of the most psychotic Mario villains of all time.
Dimentio was originally a freelance mercenary, and Count Bleck hired him for his dimensional skills after reading a passage of the Dark Prognosticus. Unlike O'Chunks and Mimi, Dimentio is pure evil and was planning to betray Count Bleck so he could rule all worlds himself. To do this, he first needed Count Bleck defeated, which could only happen if all four heroes were united with all eight Pure Hearts, so he began secretly helping them along the way.
Dimentio went with O'Chunks to Lineland where Mario, the first hero, was hunting the second Pure Heart. As the robotic dragon, Fracktail, was about to let Mario pass, Dimentio appeared and made Fracktail malfunction and attack Mario, and Mario had to destroy him to advance.
When Princess Peach was about to be brainwashed by Nastasia, Dimentio teleported her to Flipside; however, he set her high above the ground so she fell and was knocked out, in which Mario had to give her some Spicy Soup. Presumably Dimentio did the same to Bowser, teleporting him to the Bitlands, as he was not sure how he got there.
After Mimi was defeated and Mario and Peach got the third Pure Heart, Bleck sent Dimentio, who attacked Mario, Peach, and Bowser at the Dotwood Tree. He teleported them to Dimension D, which increased his attack and defense by 256 times. This, however, had no effect, as the powerup applies to everyone in the dimension, not just Dimentio. The three heroes defeated Dimentio, but he had planned this all along, and knew they would have to be stronger to defeat Bleck. He also listened in on a conversation between Bleck and Nastasia, when Nastasia tried to convince Bleck to stop the prophecy, which threatened to destroy all worlds with The Void.
When Bleck sent O'Chunks again, Dimentio once again went with him, and teleported them to Dimension D when they fought him. They defeated him, but Dimentio brainwashed O'Chunks with a Floro Sprout to turn him ino O'Cabbage. He was defeated as well, proving to Dimentio that they have gotten stronger and might be able to defeat Bleck.
While Nastasia was punishing O'Chunks for his failure, she told Mimi and Mr. L (Luigi brainwashed) that Bleck left them specific orders to stand by, as he was making a trip to confront the heroes himself. Both Mimi and Mr. L didn't like this, so it wasn't hard for Dimentio to convince them to try a sneak attack by telling them that defeating Mario would please Bleck greatly. Mimi and Mr. L were both defeated, and Mr. L's pride was damaged by being defeated twice, saying he couldn't show his face before Count Bleck again. Dimentio appeared and destroyed him by trapping him in an energy box and making it explode. However, this was only temporary; though he was sent to The Underwhere, and as Luigi, he almost immediately came back to life upon arrival. Dimentio then killed Mario, Peach, and Bowser the same way, as the seventh Pure Heart was broken and he knew only Jaydes could fix it. All four heroes were able to return from The Underwhere, as they were not truly dead (otherwise they would have become Shaydes).
Dimentio also overheard Tippi mentioning the name Blumiere, and told Bleck this to weaken him emotionally and make it easier for the heroes to defeat him, as Tippi was originally Timpani, and Bleck was originally Blumiere, and both were in love before Timpani was banished to the gap between dimensions and Blumiere turned into Bleck.
Despite the fact that Dimentio wanted the heroes to defeat Bleck, he was responsible for perhaps the hardest moment in Castle Bleck: In Castle Bleck Interior, Dimentio and several of his clones shot energy balls at Mario from the mirrors, making it difficult to jump from platform to platform. Similarly, inside a mirror in another room were hundreds of Dimentio clones; however, these were in no way a threat, did no damage and were easily destroyed by hammers and bombs.
Dimentio eventually confronted Mario and Luigi, and led them on a chase through Lineland Road, Merlee's Mansion (the Rubee stage), the Tile Pool, Planet Blobule, the Gap of Crag, the World of Nothing, and Underwhere Road. Eventually they returned to the castle and he revealed his intentions to betray Bleck, revealed his reasons for killing Mario, Peach, and Bowser, and that he rescued Peach from being brainwashed, and asked them to help him. They were not fooled by his trick and refused (he intended to brainwash them with Floro Sprouts). Dimentio decided to fight Luigi first, calling his mustache a "shag" (in the Europe version he calls him a pushover). Luigi fought Dimentio one on one, and defeated him. Dimentio created an energy box around Luigi and himself and seemingly blew them both up; what he really did was knock Luigi out and plant a Floro Sprout in his unconsciousness.
After Mario, Peach, Bowser, and Luigi defeated Bleck, Dimentio tried to kill him with an energy ball, but Nastasia jumped in front of him, killing her instead. Dimentio then assumed control of the Chaos Heart, Bleck's device to keep The Void going, and brainwashed Luigi with the Floro Sprout. After trapping Bleck, Tippi, and Nastasia's body in Dimension D so he could kill them later, Dimentio combined with Luigi and the Chaos Heart to become Super Dimentio, who was invincible, and all he needed before he became king of all worlds was to defeat the heroes, which he thought would be easy since the Pure Hearts were destroyed in the fight against Bleck to break his barrier. However, the Pure Hearts were restored by Tippi, Bleck, O'Chunks, and Mimi, and Tippi took them to Mario, taking away Super Dimentio's invincibility. Mario, Peach, and Bowser fought Super Dimentio and defeated him, destroying his body and reducing him to a head. He was shocked that they could have defeated him and undone the prophecy, however, near death, he left behind a shadow of his power to control the Chaos Heart and destroy all worlds to take everyone with him. Dimentio was completely destroyed, exploding and sinking into the ground while Luigi and the Chaos Heart were released unharmed.
However, even Dimentio's final plan failed; Tippi and Bleck got married at the altar to destroy the Chaos Heart and The Void, saving all worlds and restoring those that were destroyed. Afterward they vanished into another dimension; whether it was a paradise dimension they warped into or The Overthere is unknown; if it was the latter, it means that Dimentio indirectly killed Tippi and Bleck as well, adding them to his long list of victims.
The first time he is fought is at the Dotwood Tree, in Dimension D. Dimentio has 30 HP, 4 ATK, and 0 DEF. He will often disappear, and then reappear and attack with an energy ball. He also has the ability to create energy boxes in an attempt to trap the player, and make them explode. If he is high up, the player can avoid them and actually jump on them to get to him. When he appears, the player can jump on him. It is easier to do this with Mario or Peach rather than Bowser. Sometimes Dimentio will split into two, both of which can shoot three energy balls at once. The fake cannot be attacked, and if the real one is attacked, the fake will disappear.
Though encountered many times, Dimentio is not fought again until Castle Bleck Interior. Luigi fights him 1 on 1 without any Pixls, or Tippi. Dimentio has 80 HP, but his attack and defense are the same as before. The fighting style is the same too, except that he can split into three instead of two. Luigi can make use of his Super Jump against him.
The last time he is fought is when he is Super Dimentio, the final boss.
Dimentio is Mario's most evil enemy in the entire Mario universe, rivaling even Elder Princess Shroob. He is a psychopath, and is referred to as such by Tippi repeatedly. He often makes jokes while committing acts such as murder, which has rarely been done in the Mario series, and on other occasions in which it has, such instances have usually been either bosses pointlessly destroying their own henchmen or else eating the audience, exceptions being Hooktail and Cackletta. He directly murders five characters, and indirectly kills one (possibly three) more within the course of the storyline.
He also is extremely strategic and cunning, as he tricked Bleck into thinking he was working for him (though Nastasia apparently came to suspect him), and made sure that the heroes could face him when the time was right.
Dimentio also keeps a calm composure throughout the story, and is always making jokes, often saying several similes such as "And so I strike, like an unseen dodgeball echoing through a gymnasium", "So I arrive, like a sudden windstorm at a kindergarten picnic", or "Your blows are like miniature jackhammers wielded by tiny, angry road workers!" The only time he is truly shocked in the game is when he is defeated as Super Dimentio, but even then, near death, he regains his smile and puts into action his final plan to ensure the death of everyone all across the dimensions.
Dimentio is also a chess master, playing both sides of the battle, until Bleck is defeated and Dimentio can then put his plan to become king of all worlds into action. This gives him a slight similarity to Emperor Palpatine from Star Wars.
Dimentio will do whatever he has to do for power and control of all worlds, and is altogether evil, dark, insane, and psychotic.
Dimentio's name is derived from the words "dementia", a reference to his heavily implied insanity, and "dimension", as he is the master of dimensions.
It is unclear how his name is pronounced, however, it is hinted at when Bowser meets him for the first time and says "Dimenti-who?"
- Tippi is never around when fighting Dimentio in his standard form. The only time he can be tattled before his transformation into Super Dimentio is in the mirror room of Castle Bleck Interior.
- Tippi seems to have known Dimentio even before the events of the game. When Mario first meets him, she says "I know you. You're that..." Furthermore, after killing Mario, Peach, and Bowser, he says "You do know who I am, right? I am your enemy, Dimentio. I serve Count Bleck."
- Dimentio is similar to Fawful, in that they are both tagged as insane and psychotic, share the "always-smiling" personality, and get a similar death scene. In addition, both start out as a minion of the main villain and later become the main villain, and both take a more powerful and bigger form at the end, combined with an evil artifact. Fawful's food metaphors can be compared to Dimentio's odd similes.
- Dimentio has the appearance of a Jester from Super Mario RPG: Legend of the Seven Stars, however, his face is that of a Phanto from Super Mario Bros. 2.