The episode starts with Gumball, Darwin, and Ocho having overslept and rushing off to school. Gumball and Darwin arrive at school to find Ocho beat them, causing Gumball to ask how he got to there before they did. Ocho explains that his Uncle Mario Uncle Mario drove him to school which, after some clarification, causes Gumball to deduce that his uncle is the famous Mario and demands that Ocho marries him. After some deliberation, Gumball finally concludes that he wants to be Ocho's best friend. Darwin tries to explain how terrible of an idea it would be to manipulate Ocho, but Gumball refuses to listen. Ocho then reappears to test Gumball's trust, taking him to the school gym for a fight.
In the gym, Ocho gets involved in a fight with Bomb Guy, Rotten Cupcake, and Rat. Gumball is forced to take care of Rotten Cupcake and initially attempts to forge a compromise where he pretends to go down, but the plan fails when Rotten Cupcake instead proceeds to beat up Gumball. However, by accident, Gumball knocks him into an exercise pulley, causing the weights to fall on Rotten Cupcake and mash his face in. Gumball then plays it off as deliberate to impress Ocho.
Later, at the library, Ocho tests Gumball's ability to keep a secret by revealing his real name: Harry Tootmorsel, an Old Flemish name meaning "Hot wind from the south." Gumball tries to withhold laughter, eventually causing his eyeballs to pop out. Gumball then asks if Ocho has any more secrets, so Ocho confesses that he uses his childhood blanket as a gag when he takes people's pets hostage.
In the school hallway, Darwin argues against Gumball lending $100 to appease Ocho. After some arguing, Gumball reveals that he got it off of Richard and Nicole's credit card. Meanwhile, at the store, due to Gumball having removed the card's funds, Richard is unable to spend $1 at the grocert store. Larry tells Richard to sign up for a store credit card scheme, which he does, but the interest scheme puts Richard $121,248 (doubling by the second).
On the way home from school, Gumball is kidnapped and forced to either risk his life or Ocho's - either he jumps off of a ledge to spare Ocho or refuses and spares himself. After a botched attempt at stalling, Gumball eventually jumps, after which it is revealed that the kidnapping was a prank set up by Ocho as another part of his test. Gumball is traumatized but attempts to hide it.
As a final test, Ocho brings Gumball back to the gym and into the 'circle of trust,' presenting him with one last task- Gumball must sacrifice Darwin, giving Gumball a hammer to finish the job. Gumball ultimately hangs up pictures around the school denouncing their friendship as an alternative to presumed murder. Darwin is hurt, but through song, the two acknowledge that the declaration doesn't mean anything.
Gumball then runs off to play golf with Ocho and Uncle Mario, but upon arriving, is bummed to find that he was not the real Mario that Gumball set out to see. Darwin tries to cheer Gumball up and the two try to figure out how to terminate the relationship. Gumball ultimately settles on song, singing of how terrible their friendship was and of the measures he was willing to take to keep Ocho as far from him as possible (for Gumball's own safety). Afterwards, Ocho apologizes, having realized that he went too far because of his trust issues stemming from having another, more famous uncle in the form of "the blue hedgehog who can run really fast." Darwin tries to stop Gumball from going after Ocho again, but he runs off after Ocho regardless, ending the episode and presumably repeating the cycle.
Several references to the Mario video game franchise can be found in this episode:
Gumball asks if Ocho's uncle drove him to school in a kart, a reference to Mario Kart, and laughs when Ocho replies that his uncle has a plumbing business as Mario is typically portrayed as a plumber. Gumball then asks if he is scared by ghosts, and if he likes stars, dinosaurs, and princesses, all of which are recurring enemies, items and characters in the franchise.
Gumball says "Yahoo!" and "Let's-a go!" in an accent and intonation similar to Mario's. Additionally, he starts singing a song which resembles the Super Star invincibility theme, then mimics actions and sound effects from a typical level of Mario such as jumping on people's heads, going down a pipe, and sliding down a flag pole.
Uncle Mario wears an outfit that is very similar to Mario's outfit.
Uncle Mario's deadpan declaration of, "Hey, it's me, Mario," is based off of the character's trademark "It's a-me, Mario!"
The episode's title may be a subtle reference to the line "My uncle works for Nintendo," which has been used for decades by people who wanted to spread false information about Nintendo games.
The scene in which Ocho pretends to kidnap Gumball and potentially kill him or Ocho may potentially be a reference to a prank done by YouTube personality, Sam Pepper, in which he did a similar prank with another person tricking the latter's friend into thinking he was going to die after "kidnapping" him.
The posters announcing that Gumball and Darwin are no longer best friends are a reference to a similar Facebook post which quickly turned into an Internet meme.
When Ocho says he has an uncle who is a blue hedgehog and can run very fast, Gumball thinks of Sonic the Hedgehog. The way he runs back to Ocho at the end of the episode is also similar to Sonic's run.
When Gumball got off the bus, he was whistling the Kanto Route 1 theme from Pokémon.