3-2-1 Penguins!: The Lizard King reforms after hearing Michelle's speech on playing by the rules.
Adventures of Sonic the Hedgehog: Breezy starts out as one of Robotnik's agents and pretends she's in love with Sonic and sends him to all kinds of dangerous places(to keep him busy while Robotnik carries out his evil plan of the week), but she ends up falling for him for real after he gets her some gifts that she didn't ask for(a locket and a poem) and she's so touched that she saves Sonic from the trap that Scratch and Grounder caught him in and defects from Robotnik.
Sadira gets over her crush on Aladdin and becomes a friend of the main characters even though she had once swapped places with Jasmine, taking over Agrabah (but no-one but Iago, Abu, and Rajah remember this).
Queen Hippsodeth kidnaps Jasmine for her all-female warrior nation and then becomes Agrabah's ally because she admires the sultan for being the first person who could defeat her. The Muchtar and Aladdin's old friend-turned-monster Amal also change sides.
After Sasha and Grime stage their coup in the Season 2 finale to conquer Newtopia and the rest of Amphibia, they quickly learn that King Andrias is an evil tyrant who is planning to use the Calamity Box to take over the multiverse, and the two decide to help Anne, the Plantars, Marcy, and Frobo to stop Andrias and his robotic army. The two even try to hold him off, allowing Anne and the Plantars to escape, but are easily defeated. The Season 3 intro shows them gathering the people of Wartwood to stop Andrias.
Andrias himself also makes one in the final two episodes. After hearing Sprig read his old friend Leif's letter pleading him to keep his heart open, he relents, realizing she never stopped loving him. Seeing no other way out of the invasion he and his master the Core started, he breaks down crying and allows Anne to strike him down when the Core does a Villain Override on him. He later turns against his master by refusing to help it during the final battle, instead sending his Frobots to help the Calamity girls push back the moon and crushing hisCool Crownto bits with his remaining hand. The epilogue shows him (having abdicated his throne) and Triple B on supervised work release, replanting the flora he devastated on the Core's orders, but he's much happier now that he's free from his old master's mind control.
Arthur Binky Barnes started off as a bully, but later became a friend. To a lesser extent, Prunella also fits.
Molly and Rattles fit very well too. Originally they were even worse than Binky, but later on they became nicer.
Zuko is one of the most iconic examples in fiction, and a Double Subversion. In the second season finale, he's given tons of reasons to change sides, including an encounter with the All-Loving Hero Aang, his blooming friendship with Katara, and being put through hell all season by his sister Azula, who is prompting him to come home. It seems like Zuko will turn good... and then he doesn't, choosing to attack Aang instead and go home to the Fire Nation as a war hero. Wham!Remorse from that decision prompts him into a genuine Heel-Face Turn half a season later in "Day of the Black Sun", and Zuko being Zuko, he takes time Calling the Old Man Out before he leaves. He goes on to become True Companions with the rest of the Gaang and a key figure in taking down his father and sister.
Mai and Ty Lee follow suit in "Boiling Rock". Mai's especially was epic, showing up like a Big Damn Hero and pulling off a Moment of Awesome, while Ty Lee's just came straight from behind a tree (though disabling Azula's firebending via her pressure point techniques is still awesome).
And finally The rest of the Fire Nation after Ozai is overthrown.
One of the earliest examples in the series is the forest spirit Hei Bai. He began rampaging through a village after his forest was destroyed, but Aang reassured him that it would grow back. After that, Hei Bai was a valuable ally to Aang.
The sequel series The Legend of Korra: Desna and Eska do this in the Book 2 finale "Light in the Dark", when they join forces with their cousin Korra and the crew in order to defeat their father Unalaq (who had merged with Vaatu) and the dark spirits at the Spirit World. Cemented in Book 3, where they continue to help Korra's allies whenever need be, especially after the Red Lotus became a threat again. Varrick also follows suit, but his redemption is not universally accepted; Suyin was willing to give him a second chance, but Mako and Asami are still seething over his betrayal of them.
Later, Korra turns to none other than the anarchist leader Zaheer to help her get over the visions of him that have been preventing her from accessing her full potential after the events of Book 3. Though it is somewhat ambiguous whether Korra's enemy merely helps Korra due to their shared aversion to Kuvira, their encouraging words, genuine advice and assistance in recovering Korra's friends from the spirit world at least demonstrates that they are Friendly Enemies at this stage.
Tarrlok from Book 1 warrants a mention, since he provides Korra and Mako with the information they need to discredit his brother Amon and feels genuine remorse for his previous actions.
Parodied in one episode of The Batman, where Joker decides to become a crime fighter. Although he does target some actual criminals like Penguin, his "crime fighting" mostly consists of things like poisoning jaywalkers and little girls playing hopscotch ("graffiti").
And, at the end of the second season, the Highbreed.
Then in Ben 10: Omniverse, Zed, Khyber's former dog and the original weilder of the Nemitrex, officially becomes adopted by Kevin and joins Ben's group.
Hex also goes from being an evil sorcerer always fighting Gwen and trying to Take Over the World to a mild-mannered college professor.
Big Hero 6: The Series: Globby switches sides to the heroes at the end of series 1, horrified by the potential fallout of Obake's master plan.
The titular character of the Biker Mice from Mars episode "Hard Rock" was originally hired by Plutark to lay waste to other planets, but has now become a good guy. The Biker Mice are initially resentful toward him for the damage he's caused to Mars, but they eventually accept that he's changed his ways and help him rescue his girlfriend Darla from Lawrence Limburger.
The entire dingo family in Blinky Bill at the start of Season 2. Shifty Dingo pulls a big one in the Mother's Day episode where he helps reunite Nutsy with her long lost father.
In Buzz Lightyear of Star Command, XL, the Psycho Prototype to XR, eventually undergoes one of these; his rage against Starfleet had always been due to his belief they had abandoned him and wouldn't give him a chance, and he eventually tries to bury the hatchet. The fact he has been forcibly recruited by NOS-4A2, a robotic vampire that feeds on machinery and other robots, who keeps dropping hints about draining XL when he outlives his usefulness, further compels him to switch sides.
Foxglove from the Chip 'n Dale: Rescue Rangers episode, "Good Times, Bat Times". Starting out as a servant to wannabe witch Winifred, she is sent to pull a Honey Trap on Dale in order to steal back the list of potion ingredients for her boss. However, she quickly falls In Love with the Mark and refuses to hurt Dale and, by extension, the rest of the Rangers and fights on their side at the end of the episode.
Towards the end of "Operation P.O.O.L", all members of the DNK (except Negative Numbuh 4) go through this.
Chad in the second to last episode of the series once he reveals he was Good All Along as the KND's mole.
Mr. White stops attacking Numbuh 1 after he realizes that he can't hurt someone who folds their underwear.
Mildew Wolf was originally the scheming antagonist of the "It's The Wolf!" segments of Hanna-Barbera's The Cattanooga Cats, and was constantly trying to trick the protagonist, Lambsy, into becoming his next meal. He was later recast, in the Hanna-Barbera ensemble showLaff-A-Lympics, as a friendly (albeit cynical) sports commentator, with a strong dislike for the Really Rottens' underhanded shenanigans.
Danny Phantom: Though it never happened in the main timeline, Vlad Masters/Plasmius made one (or, at least a Heel Realization) in the Bad Future timeline after spending ten years without ghost powers. After losing everything, including the best friend he shunted aside for marrying the woman he loved (who was also lost in the same event), made Vlad realize how stupid he was being. You know it's genuine when he repairs the picture of his college days to include all three of them.
Vlad: If there was any good that came out of this, it's that ten years without ghost powers made me realize what a fool I'd been (stares sadly at the picture of him, Jack, and Maddie).
Zig-zag: In the Magnificent Muttley segment of Dastardly and Muttley in Their Flying Machines, the canine cohort of Dick Dastardly is more heroic and altruistic in his daydream fantasies as where in the show proper he's still a villain.
Dragamonz has the hero Dax's friend Boaragon forcibly undergo a FaceHeel Turn near the end of the first season. It's only after he and Dax fight, that Boaragon returns to the side of good.
After Grimserver is destroyed, Wormskull and the rest of the surviving Grimwraths also pull one of these and decide to continue battling alongside the other Dragamonz.
Downplayed in The Dragon Prince with Soren. He was never "evil," but he does get tasked by his father Viren to report that the princes have died, and if he finds them alive, "he would know what to do." Even after not going through with that, Soren still stays with his father during his invasion into Xadia (albeit after some slight mutiny saving Ezran from prison). However, Soren notices that his father was starting to become more monstrous and forcing others to become so as well, and he ends up leaving his father and joining who he believes is the true king: Ezran. His sister Claudia began on a similar path... but the way she's going is much darker.
And to another extent, Kuzco himself. Keep in mind that at the start of the film he was a bratty empreror who wanted to destroy Pacha's village to build his pool house. But after spending most of the film as a llama and forced to work together with Pacha to get back to the palace, he undergoes Character Development and learns to become a better ruler.
Xanatos is debatable. He was at worst Lawful Evil and at best a morally ambiguous Enemy Mine who would team up with the Gargoyles in cases of Evil Versus Oblivion. Xanatos is opportunistic above all else, and it could be argued that he sees the Gargoyles as valuable allies. His could be considered more of a Hazy-Feel Turn.
Arguably Macbeth as well. While he was more or less Put on the Bus after the show's second season, he did appear briefly during "The Goliath Chronicles", giving a TV interview where he defended the Gargoyles and told viewers that they were not the enemy.
Though possibly closer to Defrosting Ice Queen, Pacifica begins to go through with this in "Golf War" and makes the full leap in "Northwest Manor Mystery." Similarly, Robbie drops his vendetta against Dipper in "The Love God."
In a case of Adaptational Villainy, Teela and Duncan are both in league with the villains in He-Man and the Masters of the Universe in the beginning. Teela is a Street Urchin thief hired by Evelyn to steal artifacts related to Castle Grayskull and Duncan is the apprentice of the former royal weapons master Kronis. No one in the group is fond of how King Randor rules Eternos, but Teela and Duncan both defect from Evelyn and Kronis when their ambitions for the power of Grayskull threatens the lives of innocent people.
Tohru and Viper in Jackie Chan Adventures. Tohru's reason for changing sides is hilarious: Section 13 serves free donuts on Thursdays.
Finn, Ratso, Chow, and Hak Foo in the Grand Finale. Interestingly, the first three did make two attempts at a face-turn beforehand (in "The Good Guys" and "Dragon Scouts"): the finale was just the only attempt to stick.
In one episode of Johnny Bravo, an evil doctor and his pet kitten steal Johnny's blanket and after hearing Johnny's speech on what the blanky meant to him, the kitten makes a Heel Face Turn and attacks the doctor.
The Bee Keeper from Johnny Test pulls a rather reasonable one after Johnny, Susan and Mary find a way to get children to appreciate his natural honey candies by having him distribute them free once a year on a new holiday — they had been spending the entire episode trying to establish a new "Free Candy" holiday and continually failing due to various obstacles; ones the Bee Keeper pointed out wouldn't apply to him and his candies once he discovered their plans. Since he gets what he wanted from the beginning and the protagonists helped him do it, he's content to give up villainy.
The Brain Freezer pulls a reasonable one as well after Johnny, Dukey, Susan, and Mary help him with his looks (and other issues) long enough for him to make the ice coffee cafe he's always wanted. He doesn't exactly become a good guy, but instead a Chaotic Neutral that competes with Johnny rather than be a direct antagonist in later episodes.
Mr. Trudge in the 1980's Jonny Quest episode "Creeping Unknown" after the Quests discover the plant monster's weakness (it's sunlight, for some reason). He was only being forced to help the monster, anyway. Or so he claimed.
Vandal Savage of all people has one in Justice League, though it takes destroying humanity and living alone on the obliterated Earth for 30,000 years to make it happen: in that time he reflects on the error of his ways, learns the futility of lusting for power, and ultimately becomes a kindhearted humble person who decides to live alone on the planet as punishment for his crime. He gets the chance to Set Right What Once Went Wrong when Superman is thrust into his future by Toymaster, by helping to sent Superman back in time with information to prevent his past self from ever destroying the Earth in the first place.
Dr. Drakken and Shego in the final episode of Kim Possible team up with the heroes to save the world, and the former even wins a medal for his heroism.
In Liberty's Kids Sarah went from a fierce Loyalist to an American Patriot after seeing firsthand what the Americans went through in their fight for liberty.
The Lion Guard: Makuu pulls one in Season 2, as he starts working to become a better leader for the crocodiles and the Pride Lands. Later, in Season 3, all the animals of the Outlands make one.
Subverted in an episode of Littlest Pet Shop (2012), where the Biskit twins go through an apparent HeelFace Turn thanks to Roger's song about the joys of being nice and working hard, only to revert as soon as the song is over. The only lasting effect is that they grow to like Roger's company. Apparently they just really enjoyed singing with him, and didn't much care what the lyrics actually said.
"Prince Violent" (sometimes known as "Prince Varmint"): In his latest attempt to defeat Bugs Bunny, Yosemite Sam employs an elephant to raid an archduchy castle, which the rabbit is guarding. Sam presses his luck throughout the cartoon by threatening the elephant over his failure to stop Bugs, as the bunny is easily able to outwit both his foes. Eventually, Sam has enough and tells the elephant to get lost ("AND DON'T COME BACK!!!"). In the final segment, when Sam tries to go it alone, he succeeds in blasting the drawbridge door open with dynamite ... only to find the elephant waiting for him, as he has defected to Bugs. He even makes sure Sam understands: "I'm on the good guys side, now! So take that, bad guy," swatting him away with a club and forcing Sam to concede defeat.
The Loud House: Chandler acts as an antagonist in his debut episode, manipulating Lincoln and Clyde to give him stuff to invite them to his party. In his second appearance, he mocked the duo about a haunted house. Later, he's the one to get scared, but Lincoln and Clyde promise not to tell the rest of the school, and he shows a change of heart by inviting Lincoln and Clyde to hang out with him and his friends.
"The End of Flutter Valley, Part 10": Queen Bumble convinced to cease hostilities with the Flutter Ponies when Queen Rosedust points out that they'd be happy to share their valley's flowers if the bees stop trying to enslave them or steal their stone.
"The Glass Princess, Part 4": Porcina, who spends the bulk of the four-parter plotting to turn everything to glass so that she can have more mirrored surfaces to admire herself in, recognizes her foolishness and vanity for what they are and willing changes her ways and helps fix the damage she did.
"Crunch the Rockdog, Part 2": Crunch is evil because he literally doesn't have a heart. This lasts until the heroes get a piece of the Mountain King's heart to give him one, granting him the sense of empathy and kindness he lacked before.
"Elements of Harmony": Nightmare Moon is purified by the Elements of Harmony, and returns to being Princess Luna.
Trixie Lulamoon, a wandering stage magician, is humiliated in Season 1 when some of her fans put her false claims of magical powers to the test; Twilight Sparkle solves the problem that these fans create. Two seasons later, Trixie returns, now wielding an evil magical artifact; Twilight manages to teach her a lesson once again, and Trixie leaves on semi-good terms... although the nature of her apology suggests that she's not quite one of the good guys yet. Trixie's turn finally solidifies in Season 6 when she finally gets a real friend in the form of Starlight Glimmer, another unicorn in the middle of her own HeelFace Turn, and nearly loses it because of her petty desire to one up Twilight. At the start of Season 7, Trixie is now shown to be fully on the side of good.
"Crusaders of the Lost Mark": Diamond Tiara, who for most of the show's run is a fairly straightforward schoolyard bully and upper-class snob, becomes friends with the Cutie Mark Crusaders.
Starlight Glimmer, introduced in Season 5 as a G-rated cult leader obsessed with making everyone equal by making everyone equally plain and untalented, becomes a Sixth Ranger for the Mane Six in the Season 5 Finale.
Ninjago: Early in the show, Lloyd Garmadon, the son of malicious Lord Garmadon, tries his best to be a villain, but in hindsight, he's just a mischief-making little kid. After many mishaps and his worst mistake of all, releasing Pythor, Sensei Wu decides to put Lloyd back on track by treating him as if he were his own son. Lloyd drops the "bad guy" routine in a heartbeat, but still remains a troublesome prankster.
Garmadon himself gets redeemed after Lloyd wins the first battle with the Overlord, purging all evil from his body and reverting him back to his original human appearance and personality. Now The Atoner, he joins his brother Wu as a mentor for the ninja and rebuilds his relationship with his son.
In Day Of The Departed, Morro opts to warn Sensei Wu about Yang's plan to kill the ninja and take their place among the living instead of fighting him like the other resurrected villains. The reason for his sudden HeelFace Turn traces back to the circumstances of his death as a ghost in Season 5, in which he rejects Wu's offer to save him from the Preeminent.
Lilith, the Arc Villain of season 1, pulls one in the first season finale. After Belos reveals he lied to her about healing Eda's curse, Lilith realizes she made a terrible mistake, rescues Luz, and then goes on to help rescue Eda from petrification as well. In the end, she shares the Owl Beast curse with her sister, and formally comes to live in the Owl House.
While Hunter remains an antagonist for most of Season 2, he slowly starts to warm up to the protagonists through multiple Enemy Mine situations and joining their sports team while undercover. He formally defects from the Emperor's Coven after learning the truth about the Day of Unity, and the fact that Belos tried to kill him after he learned he's actually a Grimwalker. He initially runs away from the Owl House, but is found two episodes later by Gus, and formally joins the protagonists as he saves Gus from Graye and tells the other students what the Day of Unity actually is.
In the Grand Finale of Phineas and Ferb, Doofenshmirtz realizes that he doesn't really want to be evil and decides that he's going to be a good guy from now on. This is reinforced by two earlier episodes. In Doof 101, it's revealed that OWCA placed Dr. D as a high school science teacher as community service/rehabilitation, to which he seems genuinely happy in. In Act Your Age, which takes place 10 years later, it's revealed that he is still happy as a science teacher, is friendly with Monogram, and even goes bowling with Carl and Perry.
In ReBoot, Hack n Slash are a prominent example, joining the protagonists after Megabyte gets them destroyed and Phong rebuilds them, and them realizing that they missed having Bob around to stop them before they actually did anything really bad. Hexadecimal also undergoes profound change in the latter seasons.
Wouldn't you switch sides if your enemy put you back together after your boss sent you to the front lines to get destroyed by his sister simply to get rid of you?
In Rise of the Teenage Mutant Ninja Turtles, after Season 1's Big Bad Baron Draxum (who created the Turtles in this iteration) is defeated, Mikey, seeing Draxum as part of the TMNT family in spite of everything, saves Draxum from destitution and helps him turn over a new leaf — and good thing, too, since Draxum is now a powerful ally to the Turtles, having gotten them out of dire situations a number of times.
Da Samurai went through this to an extent after fighting Jack, although he was less evil and more of a dick.
Ashi was put through Training from Hell ever since birth for the sole purpose of killing Jack. However, when she fails, he not only spares her life but take pity on her, and works hard to break her free of her conditioning. Between his constant kindness, and being forced to see the true nature of Aku's effect on the world, she finally accepts the truth, and joins Jack's side.
The entire plot of She-Ra and the Princesses of Power came about because Adora, when confronted with the atrocities committed by the Horde, refused to go back to them and stayed in Bright Moon instead. And in Season 4, Scorpia realises that between Catra's betrayal of Entrapta and the deal her family made with the Horde being pretty awful, she can't stay in the Fright Zone, and eventually makes it to Bright Moon, joins the Princess Alliance, and befriends Frosta and Perfuma.
In Season 5, Catra in a case of Love Redeems from Adora, followed by Wrong Hordak during the season and ultimately, Hordak in the Grand Finale after Adora manages to free him from Horde Prime's control.
Adora's turn is strongly deconstructed. While her new friends in the Rebellion warms up to her rather quickly, her old friends in the Horde are left bitter and resentful for her betrayal. It doesn't help that she made the decision rather quickly without talking to them at all first, making it nearly impossible for her to reach out to them afterward.
"Gorgeous Grampa" played this trope closer to its origins, as Abe's wrestling character, a notorious Narcissistheel called "Glamorous Godfrey" turns into a face named "Honest Abe" right in the ring when he found out Bart was loving the heel lifestyle a bit too much.
"Bigmouth's Friend": Bigmouth, the Hulk Speak ogre who lived in the Smurf Forest, was more an Anti-Villain and Ineffectual Sympathetic Villain, although he did menace the Smurfs on several occasions, often to try to gain favor with Gargamel, whom he looked up to. But in this episode, Bigmouth finally realizes Gargamel and Lord Balthazar are not his friends and simply want him to do more than just go away ... and when he sees his Only Friend Clockwork Smurf get crushed into splinters by Lord Balthazar (during an attempt to overthrow King Gerard), he turns to the side of the Smurfs (his real friends) for good and helps them stop Balthazar.
In Star vs. the Forces of Evil, Buff Frog, who was originally one of Ludo's most trusted companions, ends up helping Star rescue Marco from Toffee, trusting Star with babysitting his babies, and even turning down the chance to rejoin Ludo's ranks when he regained power. The fact that he decided to warn Star about the incoming threat afterward confirmed his complete heel-face turn.
Nossor Ri and the entire Quarren army at the end of the Mon Calamari Arc in Season 4.
General Tandin and several of his soldiers in the Onderon Arc in Season 5.
After being "fired" by Count Dooku on Palpatine's orders, Asajj Ventress eventually develops into an Anti-Hero.
Star Wars: Rebels: The events of Season 2 episode "The Honorable Ones" end up triggering one for Agent Kallus. By the beginning of Season 3, after a Time Skip, he's become a mole in the Empire. At the end of the season, after being exposed, he manages to escape and properly join the rebels.
Rubberband Man in Static Shock. Near the end of the series, when a cure to the mutagen gas has been made, so do Aqua Maria and Talon.
In "Message Received", Peridot, a Gem Homeworld technician who opposes the Crystal Gems in her early appearances and later forms a truce with them to save her own skin, ends up becoming the Sixth Ranger of the Crystal Gems after realizing the Earth has things worth protecting from the ambitions of her superior, Yellow Diamond.
In the Season 5 finale "Change Your Mind", Blue and Yellow Diamond make one upon realizing how awful they've been to Pink and the Homeworld Gems, and WhiteDiamond makes one after she realizes she's not flawless and Steven convinces her to accept people for their flaws in order to truly rise above them.
Super Dinosaur: In "Out of Our Depth", after being betrayed by the Shark-Men, having to work with Derek and SD, and being saved by the latter, Squidious realizes that not all humans are terrible people and decides to help Earthcore against Minimus.
Super Friends. This happened at the end of almost all of the 1973/74 episodes after the Super Friends explained to the villain(s) the errors of their ways. It usually involved the villain sincerely apologizing and promising to change their behavior. Examples: Doctor Rebos in "The Androids", Professor Baffles in "The Baffles Puzzle", Minimus Mole in "The Mysterious Moles", Anthro the alien in "The Power Pirate" and Dr. Shamon in "The Shamon U".
Tangled: The Series: Varian undergoes a pretty devilish FaceHeel Turn in mid-Season One, doesn't appear in Season 2, and returns to the side of good in the Season 3 premiere special. His return to goodness doesn't come without a hell of a lot of guilt and trauma over what he'd previously done, however.
Also, Cassandra at the series finale. She goes through a FaceHeel Turn in the Season 2 finale, spending Season 3 as an antagonist, before finally becoming good again by the series finale, helping Rapunzel to defeat Zhan Tiri.
Teenage Mutant Ninja Turtles (2012)'s incarnation of Slash is depicted as a Well-Intentioned Extremist, who wants what he thought was best for Raphael by killing his brothers. After being defeated, he fled and joined forces with the even more psychotic Newtrailzer in fighting the Kraang. However once Newtralizer's plan of Kraang-eradication involving killing several innocent humans, Slash became disgusted and ultimately re-joined Raph in taking him down. Mild example, but very apparent by his more heartfelt parting with the turtles.
Toxic Crusaders has this with the two-headed Toxic Crusader Headbanger (Dr. Bender and Fender), who were originally on Dr. Killemoff's side, but joined the Toxic Crusaders after deciding that it would be more fun to be the good guys.
Transformers: Beast Wars has a number of examples. Dinobot and Silverbolt spent relatively little screen time as heels, but Dinobot was a pretty slagging well-done heel. More literal examples are: In the third season, Blackarachnia, and, near the end of the series finale, Dinobot's Transmetal 2 clone.
In Transformers: Armada, Starscream (who seemed to be more based on Dinobot than the original Starscream) switched sides to the Autobots once Megatron got fed up with him being The Starscream. While Starscream originally only joined to stick it to Megatron, he hit it off with the kids and slowly became more accepted. Later, he would turn evil again and flop around to every "side" imaginable on the show. Eventually, he decided the threat of Unicron necessitated all of the Transformers uniting together and sacrificed himself to make Megatron realize that. He was recognized as a hero for his dying actions.
G1 has Jetfire/Skyfire (comics and cartoon, respectively).
In the cartoon, Skyfire (renamed due to the changes made to his animation model to distance the character from his toy's Macross roots) was a non-aligned Transformer from before the war, and old friend and colleague of Starscream's, who was lost when the two were deep space explorers visiting prehistoric Earth millions of years before the Ark crashed on it. When the Decepticons found him frozen in the Arctic, Starscream initially convinced him to join them, but the Autobots and their human allies convince him to turn against the Decepticons.
In the Marvel comics, Jetfire (using the toy's name but still having the animation model) was built on Earth by Shockwave, but Buster was able to gain control of him using the Creation Matrix and free Optimus Prime, who later used the Matrix to give Jetfire life as an Autobot.
Predacons Rising had two. The first one being Knock Out, in which it took some time for him to finally act like a true Autobot. The second one is Megatron, of all Decepticons. Having felt true oppression through Unicron's possession of his body, Megatron no longer wished to inflict it himself, and thus disbanded the Decepticons, then left for parts unknown.
Subverted with Sergeant Hatred from The Venture Bros.. He switched sides, going from an antagonist to a protagonist. However Venture Industries is just as immoral as the Guild, it's just the Guild admits and embraces this, whereas Dr. Venture doesn't even realize this. (Though at least he's trying to quit being a pedophile.)
Taken in a dark direction with Gary (formerly known as 21), he joins SPHINX and quits working for the Monarch. Yet The Monarch misses him so much, he's in denial about it and still thinks he's working for him. While Sgt. Hatred didn't trust him because he also thought he was still a henchman of the Monarch and the rest of SPHINX wasn't sure about him either at first. Gary, after realizing Good Feels Good, also went out of his way to catch a bad guy even though no one told him to, only to ruin Brock and Shore Leave's undercover mission. It's implied in-series this happened more than once by Hunter which causes Hunter to want him off the team. Sooner-or-later Gary accidentally hiring the old SPHINX back, making it so that they steal their mode of transportation and try their hand at evil once again and feels guilty about this. And Brock and Shore Leave end up feeling sorry for him because of it. In the end he decides to start henching for the monarch again.
Played straight with Acxa in the three-year gap between Seasons 6 and 7, who refused to take part in Zethrid and Ezor's plans to become space pirates with the intent of torturing prisoners; instead opting to find her own path, which results in her helping Team Voltron and later joining the Voltron Coalition.
In Season 8, Zethrid and Ezor redeems themselves and in the end joins the Blade of Marmora along with Lahn, the Beta Traz Warden, the Altean Empire and the Galra Empire, while it's a Death Equals Redemption for both Zarkon and Lotor in the five-part finale along with a Redemption Equals Death for Honerva in the same finale.
Rax, Nyma and Rolo went from working with the Galra Empire to being allies to Team Voltron.
Wander over Yonder: Happens several times at the hands of Wander to Westley, Destructor, Beep-Boop, Something-the-So-and-So, and the Black Cube of Darkness and, before the events of the show, Major Threat.
Surprisingly, the same thing also happens to Sylvia before the events of the main series.
Xavier Riddle and the Secret Museum: Sarah, the racist little girl, undergoes this in "I Am Jackie Robinson", when Jackie (who she was mean to) shows her kindness. This also happens to Brian, the kid who wouldn't let Yadina play on the swings.
Xiaolin Showdown: Raimundo, although that's after he did a FaceHeel Turn. He actually does suffer some consequences and trust issues afterwards because of it.