"I am a humble servant of Count Bleck. Master of dimensions, pleaser of crowds, I am... Dimentio!"
Dimentio is a magical jester and main antagonist in the game Super Paper Mario. He initially seems like just another servant, but as the story progresses he is slowly revealed to be much more sinister and manipulative than even his own master.
Dimentio's past is largely unknown, however apparently he was the one to approach Bleck and offer to become his servant, contrary to how Bleck's other minions joined him. Dimentio's abilities include flipping dimensions (which he can control) and teleportation of himself and others. He can also clone himself up to twice in battle, and seemingly more outside battle (as evidenced by a hallway in Castle Bleck that is completely filled with his clones). However his clones are significantly weaker and are destroyed by a single hit.
Dimentio first appears in an interlude before the first chapter of the game. He, along with Mimi and O'Chunks, are in a meeting with Bleck and his assistant Nastasia. He casually embarrasses Mimi in front of everyone by stating something he found in her diary, which she unintentionally confirms by yelling at him for reading it. Bleck then decides to send O'Chunks to hinder Mario's progress, and Dimentio decides to tag along.
Though Dimentio does not appear to assist O'Chunks in his first boss fight, he appears later, at the end of Chapter 1, interrupting the robot guardian Fracktail and using magic to cause it to attack Mario. Due to Dimentio's interference Mario is forced to destroy Fracktail, who only comes to his senses when he is about to explode.
Dimentio is later sent by Count Bleck to attack Mario, Princess Peach and Bowser at the Dotwood Tree in Chapter 3. He transports them to his own realm, Dimension D, where he claims he is 256 times more powerful. As it turns out, he isn't the only one affected by this power boost, thus negating any advantages of either side. Once defeated, he reveals that it was only a test and that he would be much deadlier next time. On the way back to Bleck's Castle, Dimentio is seen muttering to himself about how he must make sure the heroes have the strength to face the count when the time comes.
During the interlude following Chapter 4, a new minion is introduced to the villain team: Mr. L, who is actually Luigi under the mind control of Nastasia. When Count Bleck mentions a prophecy about a "man in green" being the one to bring darkness to all, Dimentio considers the possibility that Mr. L is in fact, the prophesied Man in Green. Bleck then sends O'Chunks off to deal with the heroes again, and once again Dimentio accompanies him. This time, Dimentio assists O'Chunks by allowing the battle to take place in Dimension D. Nevertheless, O'Chunks is still defeated and contemplates suicide. However, Dimentio convinces him to help out with a mysterious plan that will supposedly aid Bleck, and they leave. The heroes encounter them once again in the Processing Center located in Floro Caverns. Dimentio reveals that he has negotiated with the Floro Sapiens' king, Croacus IV to obtain some Floro Sprouts, one of which he plants in O'Chunks's head. O'Chunks begins beating his chest wildly and shouting the names of random vegetables. Once again, Dimentio transports them to Dimension D, but even with his more unpredictable movement, O'Chunks is defeated and the sprout falls off his head.
In the following interlude, Count Bleck is not present in the castle and has left orders for all minions to stand by. Mimi and Mr. L express their desire to fight the heroes again but resist the urge until Dimentio enters and tempts them with the prospect of defeating the heroes and pleasing the count. Both proceed to make quick excuses to leave, and Dimentio follows them. The setting of Chapter 6, Sammer's Kingdom, is on the brink of destruction and after being stalled by Mimi, Mario and friends fail to make it to the Pure Heart in time, and end up back in Flipside as the kingdom is sucked into The Void. Upon returning, they find that the once-great kingdom was now a white span of nothing. They eventually find the Pure Heart, the only thing that survived the destruction, which was badly damaged. It is stolen by Mr. L however, and the heroes battle him for it. Once they leave, Dimentio finds Mr. L in the world of nothing, frustratingly muttering about his failures. Dimentio decides that it's best to be rid of Mr. L here, where no one will find him. Trapping the masked man in a magical box, he causes a massive explosion, seemingly killing Mr. L, before teleporting away.
Dimentio then heads for the house of Merlon, who the heroes were consulting about the damaged Pure Heart. He then repeats the same spell he used to destroy Mr. L on Mario, Peach and Bowser. Mario finds himself in The Underwhere, where he meets up with Luigi. The Queen of that realm, Jaydes, is able to restore the Pure Heart and allow the brothers to escape.
Dimentio returns as the boss of the third segment of Chapter 8, the final chapter. Previously, Bowser and Peach had battled O'Chunks and Mimi, respectively, before being trapped and unable to move on. When Mario and Luigi confront Dimentio, he first plays a game with them in which they have to chase him through a small segment of every previous chapter. Once they arrive back at Castle Bleck, he reveals that he had been secretly assisting the heroes the whole time. It is revealed that Peach and Bowser's escape of brainwashing was by Dimentio's hand, as well as Luigi being set free from the evil "Mr. L" persona. However, Tippi senses that Dimentio is still up to no good, and convinces the brothers to refuse to join him. Agitated, Dimentio threatens to "end their games," starting with Luigi because his mustache is shaggy. Luigi is greatly offended by this, and insists to battle Dimentio alone while Mario runs ahead. Mario reluctantly agrees, and Luigi defeats Dimentio in battle. Dimentio, remembering the prophecy about Luigi, decides to prevent him from continuing by faking a double suicide. Sealing the door forward shut, he traps himself and Luigi in a box and proceeds to blow it up.
Mario is forced to face Count Bleck alone, but is no match for the count's impenetrable force field provided by the Chaos Heart. Just when all hope is lost, Bowser, Peach and Luigi find their way in. The power of the four heroes uniting is enough to spawn the Pure Hearts and negate Bleck's force field. They proceed to defeat the count, who then fully reveals his motivations and backstory, including his tragic relationship with Tippi. Before accounts can be settled, however, Dimentio fires a beam at Bleck, which Nastasia blocks with her own body, knocking her out. Dimentio then reveals his true nature: a manipulative backstabber who was only in it for his own gain from the beginning. He explains how he only helped the heroes so they could defeat Count Bleck with the Pure Hearts, allowing Dimentio to steal the Chaos Heart. Then he uses the last Floro Sprout to brainwash Luigi again, turning him into a submissive zombie. He then combines the Chaos Heart with Luigi, possessing the resulting entity to form Super Dimentio. The remaining heroes attempt to fight him, but he proves too powerful and brags about being invincible and how they wasted the Pure Hearts on Count Bleck. Dimentio laughs as he provides more power to the already-massive Void, allowing it to consume several more worlds.
Count Bleck and Tippi, who were sent to Dimension D to presumably be tortured and killed by Dimentio later, are joined by O'Chunks and Mimi. The love between Bleck and Tippi and the loyalty of O'Chunks and Mimi is enough to rekindle the power of the Pure Hearts, which Tippi uses to escape and rejoin Mario, Peach and Bowser. They use the Pure Hearts to weaken Super Dimentio, much to his utter dismay, and destroy most of his body. The now-unstable head of Super Dimentio begins to laugh maniacally and talk about how he is saving "one last surprise" before exploding and releasing Luigi and the Chaos Heart. The heroes are then joined by Bleck, Mimi and O'Chunks, who reveal that Dimentio must have left behind a shadow of his power to continue fueling the Chaos Heart. Though small, Bleck explains that it may be enough to finish destroying all of existence. At this point Bleck instructs everyone to follow him into the castle's chapel, where he and Tippi confess their love for each other one last time, allowing the Pure Hearts to counter the Chaos Heart at the cost of their lives. As a result, the Void is closed and all destroyed worlds are restored, permanently erasing all of Dimentio's evil work and negating the power of the dark prophecy.
While Dimentio hasn't physically appeared in any other official media, he is mentioned in Fracktail's trophy description in Super Smash Bros. for Wii U which outlines the events of Dimentio causing the peaceful guardian to turn hostile. He does have a cult following in the fanbase, much like Fawful from the Mario & Luigi series, for his surprisingly dark actions (especially for the family-friendly Mario franchise) and how he came frighteningly close to ending all of existence and rebuilding it in his own image. He is often regarded as the Mario equivalent to Kefka Palazzo of the Final Fantasy series. Many fans want to see him return in some form.