Inverted in Avatar: The Last Airbender, where Zuko's father is the evil, younger brother who stole the throne, while his uncle is a genuinely nice, caring person. Zuko himself said his uncle was more of a father figure to him when he was Calling the Old Man Out. Interestingly, though, Iroh was originally this while the show was still in design. Before he was redesigned into the tea-loving, Pai Sho playingBig Fun that we all know and love, he would have taught Zuko incorrect firebending on Ozai's orders and fought Zuko in season 3. Ozai would've become this to Lu-Ten, Iroh's late son.
Played straight in The Legend of Korra with Unalaq, Korra's uncle. Not only does he fix the trial to get his brother Tonraq sent to prison for life, but he also arranged for him to be exiled by paying barbarians to attack the city and hide in the spirit forest, which Tonraq destroyed. When Korra learns this, she turns against him and calls him out on his jealousy. He also trained Korra for his own desires - unlike Iroh, who genuinely cared for his nephew Zuko. Not only that, but he appears to be a neglectful father to the Creepy Twins Eska and Desna as well, such as leaving an injured Desna on the ground just to try and open the Spirit World portal. The contrast between Iroh and Unalaq becomes more evident in the episode "A New Spiritual Age", when both appear in different moments and interact with Korra. Then he fuses with Vaatu, becoming Korra's Evil Counterpart, the Dark Avatar.
Double Dragon (1993): The Shadow Master. In one episode, Mrs. Lee, the mother of Billy and Jimmy makes an appearance. She reveals that not only is she their mother, but the main villain, the Shadow Master is none other than her brother, making him the twins' uncle.
The original 1993 series revealed the main villain Lawrence Lactavius Limburger to be an uncle in the episode "Modo Hangs it Up", although his nephew Marshall is even worse.
The 2006 revival episode "Swimming with Sharks" introduces Vinnie's maternal aunt Mago, who is a space pirate who wants to kill Stoker for becoming leader of the Martian freedom fighters instead of her. She also attempts to make a deal with her nephew, Throttle, and Modo to rehydrate Mars by beaming all of Earth's water to the planet, a deal that the Biker Mice obviously refuse.
Masters of the Universe: A reference in the tie-in comics indicates that Skeletor is actually King Randor's long-lost brother Keldor, which would make him Prince Adam/He-Man's uncle.
In Batman: The Brave and the Bold, Aquaman's first episode features his brother, who despite having rebelled against him in the past, is accepted back some years later. He immediately tries to usurp Aquaman's crown again.
The Weird Al Show: In the animated "Fatman" segments, Fatman has an Evil Uncle Frank who was intended to be a recurring villain.
It's revealed in Operation: Z.E.R.O. that Father (AKA the Big Bad in the series and archnemesis to Numbuh 1) is Benedict Uno, and that he and Monty Uno (Numbuh 1's father) are both brothers.
An official comic story reveals the Toiletnator, the show's resident Ineffectual Sympathetic Villain, is Numbuh 4's long-lost uncle.
Felix the Cat: The Professor is an enemy of the titular cat, but his nephew Poindexter is friends with Felix.
"Reign of the Boy King": Black Duke Lucan wants to usurp the throne of Morovia from his nephew King Alexander.
"Robot Raid": Merick wants to prevent his niece Jennifer from inheriting the family's company.
Punky Brewster: Punky discovers she has an aunt and an uncle in "Punky the Heiress," and they've offered to reunite her with her missing mother. But (a) they're actually servants for the Chester Henderson estate, and (b) they're using Punky to embezzle the inheritance of Henderson's granddaughter, of whom they have Punky dressed up to look like.
All Hail King Julien has Julien's uncle, King Julien XII. In the pilot, he passes the crown to his nephew because the king was predicted to be sacrificed to the fossa. He returns in the fifth episode to take back his reign, sending Julien to be unwittingly eaten by the fossa, and removes all the fun things his nephew did for the kingdom.
The Smurfs (1981): King Gerard has his aunt Imperia and his uncle Sir Leopold, both evil and both desiring to go after their nephew's throne.
In Jonny Quest: The Real Adventures, the sequel to the 1960s series, Hadji is revealed to be a prince and back during his childhood, his uncle and cousin wished to kill him so they could usurp his family's kingdom. Fortunately, the assassin they hired, Pasha, couldn't bring himself to kill (the then-four-year-old) Hadji and just took him away to save them both. Hadji's uncle, Deepak, soon took over after his brother (Hadji's father) passed away from an illness, but later in the future, Hadji's cousin, Vikram, eventually kills his father and becomes sultan. When Hadji returns home to find Pasha, Vikram attempts to kill him, but winds up getting his just desserts, allowing Hadji to take his birthright, which he shares with his mother.
Casper the Friendly Ghost: How evil they are may depend on the writer, but the Ghostly Trio are Casper's uncles (and in some continuities guardians) and always portrayed as much meaner than him. Wendy's witch aunts are the same case with the genders inverted.
Time Warp Trio has Mad Jack, twin brother of the main character's Uncle Joe who gave him The Book. He wants to steal it for himself in order to Take Over the World and is willing to off anyone who gets in his way, including his ten-year-old nephew.
In The Crumpets, the titular family were frequently swindled by Uncle Hurry and Aunt Harried, who were Pa Crumpet's brother and sister-in-law.
In Princess Natasha, Natasha's arch-nemesis is her uncle Lubek who seeks to take the throne of Zoravia for himself. Natasha is a teenage princess of a foreign country who is transferred to the United States to be a secret agent as a student of a high school, where her evil uncle is the principal.
Actually downplayed with Ocean Master, mostly because he's Out of Focus. He does try to kill his nephew, along with many other children, in "Home Fires", though more out of revenge than a hope of actually getting the throne.
Count Vertigo apparently killed the old king of Vlatava (relation to him unknown) and now wants to do the same to his niece, Queen Perdita. This is a change from the comics, where he's the last member of the Vlatavan royal family and wants to overthrow its republican government.
Baron Bedlam is this to the Markovian royal family, killing his sister and brother-in-law and then trying to steal the crown from his nephew, Gregor. Like Vertigo, this is an adaptational change; in the comics he's not related to them at all, his family just replaced them as a puppet government for the Nazis.
Garfield and Friends: Orson's older brothers Mort, Gort and Wart in the U.S. Acres segments are a bunch of gluttonous brutes who try to steal the gang's harvest and could technically be considered Booker and Sheldon's uncles, since Booker and Sheldon are Orson's adoptive sons.
The Owl House has Big Bad Emperor Belos, whose nephew Hunter serves as his Dragon, the Golden Guard. Belos is extremely abusive towards Hunter, including giving a 16 year-old the workload of a grown adult, repeatedly threatening to throw him out onto the street, blaming Hunter's failures for his curse worsening, never allowing him to leave the castle unless it's for a mission, and based on the way Hunter flinches at unexpected touch, it's heavily implied Belos is physically abusive towards him as well. Of course learning the truth about himself doesn't improve Hunter's situation in the slightest — Hunter and every Golden Guard before him are magical clones called Grimwalkers, cloned from Belos's brother Caleb, who was murdered by Belos after marrying and having a child with a witch. Whenever a Grimwalker "betrays" him, Belos kills them and replaces them with a new one. Hunter only very narrowly manages to escape with his life, and is forced to go on the run as Belos sends the entire Emperor's Coven after him. Later in "Thanks to Them", Belos somehow manages to top his earlier abuses of Hunter by straight up possessing the kid and using his body to kill Flapjack, Hunter's Palisman.
101 Dalmatian Street has a much older Cruella de Vil become an evil great aunt to a boy named Hunter. She manipulates him into helping her capture the descendants of the original Dalmatian family from the 1960s, all while abusing, neglecting, and ultimately abandoning the boy when she no longer deems him useful.
