Prismo is a Wish Master who is the manifestation of an old man's dream. First mentioned in "The Lich," he plays a major role in the episodes "Wake Up," "Jake the Dog," "Is That You?," and "Crossover." He resides in the Time Room, which is found in the center of the multiverse. Booko describes him as "almighty." Prismo is apparently good friends with a number of cosmic-level characters in the Adventure Time universe, including the Cosmic Owl, Party God, Death, and Grob Gob Glob Grod, all of whom were seen at one of his Time Room parties.
He is revealed to be the dream-projection of a sleeping old man in "Wake Up." He sends Finn and Jake to retrieve his mortal body to wake him up, thereby committing a cosmic crime and summoning a Citadel Guardian to take them to the Citadel to find Finn's human dad, Martin. Prismo explains he will vanish when his mortal body wakes up, but figures he will reappear once that body goes back to sleep in 1000 years. Unfortunately, the Lich takes advantage of the situation by waking up Prismo's mortal body and reducing it to ash, killing Prismo.
In "Is That You?" Finn and Jake perform a memorial ritual centered around the last of Prismo's pickles. Through a series of time-bending dream sequences involving a past version of Jake becoming the sleeping old man that Prismo resides in the dreams of, Prismo is brought back to life.
Prismo is shaped like a giant humanoid shadow with blue eyes and can move on walls, his body sticking to whatever it's on. Essentially, he's two-dimensional. As an old man he is a small humanoid with a large beard and dark brown skin.
Prismo is a very considerate and friendly being, demonstrated several times throughout the episodes he was in. He gives Jake advice about what wish to make and throws parties in his Time Room. Despite his omnipotent power, he is far from being aloof and indifferent towards mortals and is in fact the exact opposite; he even goes as far as to fully explain to Jake any potential consequences after granting a wish. Prismo does, however, get mildly annoyed when his relationship with those who visit him in his Time Room gets questioned (he would defend himself by saying that he does have friends) or whenever someone makes petty wishes of him when they should be wishing for something appropriate for the circumstances. He is generally nice to the people he meets, as shown when Finn and Jake first enter the Time Room, and is even willing to sacrifice himself for the needs of his friends, demonstrated when he tells Finn and Jake they can "kill" him (wake up his corporeal form) in order to reach the Citadel.
Prismo can grant any being in the multiverse one wish. However, he can apparently refuse benign or even neutral wishes (in short, those that are mundane and "small-scale") in favor of those by his recommendation. Once the wish is granted, the wisher is transported into his/her wish-altered reality. These wishes are powerful enough to change timelines and create or destroy worlds. However, unless worded very specifically, his wishes usually have an unpredictable twist, since the wish often changes the timeline, or brings in an unwanted element.
Prismo can also create material items for himself and others without it counting as a wish, like food and a hot tub, as seen in "Jake the Dog" and "Wake Up."
Prismo is seen with the Cosmic Owl, and the two appear to be friends. The Cosmic Owl comes to hang out with Prismo in the Time Room while Jake is there, and he implies that he has done this in the past. In "Wake Up" Cosmic Owl leaves Prismo's time room in a hurry after hearing Finn and Jake needed to kill a cosmic entity.
Prismo grows close to Jake while Finn is suffering the consequences of his wish, and he helps Jake resolve the universe by telling him what to wish for. Jake says that Prismo is a "strong number three on [his] Cool Guys List." Prismo later sends Jake a jar of pickles with a note, which says that he wants to hang out with Jake more. Jake insists that he has to get Prismo a girlfriend. In "Wake Up," Jake tells Prismo that he always smiles around him, with Prismo telling him he feels the same. Later, when The Lich kills Prismo's mortal body (with his breath), Jake becomes furious and grows large and muscular, declaring that he will kill The Lich for killing Prismo.
In "Is That You?", Finn sums up his relationship to Prismo when he says "Heroes risk everything for their friends, although, I admit, you're more Jake's friend than mine. Sometimes you can think someone is totally cool, but you never become besties. And I don't know why that happens, but regardless, let's do this."
In "Hoots", The Cosmic Owl even mentions Finn's name. Prismo even hesitated to know who he was and even questioned if he knew him or not which really implies that he is way closer with Jake than he is with Finn.
- Prismo has his own homemade pickle brand, "Prismo's Homemade Artisanal Pickles" as seen in "Jake the Dog."
- Prismo is profiled as a "wish master" in the T.V. Guide description of "Finn the Human." Prismo also refers to himself as such in "Wake Up."
- Prismo says that he gets out of relationships because he does not want to bother about discussing what to eat for dinner every night.
- Prismo was a lighter shade of pink in "Finn the Human" than in "Jake the Dog." He also didn't have teeth whenever he speaks until "Crossover." His eye is much smaller than it was in the aforementioned episodes.
- Prismo can create anything he wants with colored magic cubes, such as a jacuzzi, cheesy crackers, pickles, a remote, and an egg.
- As stated in "Finn the Human," once Finn made his wish, he was transported to his wish-altered reality; this new reality (i.e. Farmworld) should have replaced Finn's previous existence, but because Jake was still in the time room (a place wherein beings are not affected by wish-altered realities), a memory of Finn as he was in the prime universe existed in tandem with Farmworld Finn (in other words, a paradox was created, because Jake remembered the original Finn while Finn also existed in a wish-altered state in Farmworld). After Jake made his wish, Finn was returned to the prime universe, but Farmworld continued to exist, due to the aforementioned paradox.
- In "Wake Up," Jake touches the "P" on the note Prismo left him at the end of "Jake the Dog," which transports him to the Time Room.
- Prismo was the dream of an old man, and Prismo's dream form hung out with the Cosmic Owl. The Cosmic Owl occasionally appears in the dreams of those who are going to die, so his death was technically predicted.
- It could be inferred that Prismo has a son somewhere in the Multiverse: after being abruptly awoken by The Lich, Prismo asks if he is his son. If this is true, he must have dated someone in the past.
- Prismo plays the banjo, as seen in "Hoots."
- In "Crossover," he reveals that he does have a boss, but gives no further explanation of it.
- He made the Card Wars kingdom for Jake.
- Prismo twice refers to the classic horror story "The Monkey's Paw" when attempting to explain the unintended perversion of the wish's outcome on reality.
- Prismo is similar to a genie in that he can grant wishes.