The Grinch used to be evil by stealing Christmas, but later noticed that Christmas means a little bit more.
The Beast was introduced as a spoiled, grouchy, mean prince who knows nothing of love, but he proves himself a compassionate and selfless hero who can't live without his true love Belle.
Iago started off in the first Aladdin movie as Jafar's sidekick, but in The Return of Jafar he becomes fed up with Jafar's abuse and abandons him. He joins the heroes for his own gain, and eventually starts to actually like them. At the climax, Iago ultimately redeems himself by kicking Jafar's black lamp into molten lava, destroying him forever. The fully redeemed parrot is then finally accepted into the palace.
Jack Skellington was an anti-hero who did his job every Halloween when he takes over Santa Claus' job and ruined Christmas. He realized he made a big mistake and should've listened to Sally, after saving her and Santa, he still remains the Pumpkin King of Halloweentown.
Discord was evil and malevolent master of chaos, but much later he reformed and befriend with Ponies of Equestria.
Gru was a supervillain who plotted to steal the moon and was intent on using Margo, Edith and Agnes in his plan, but grows to love them and grows from an evil genius to a compassionate father.
For most of the time, Shero was nasty, violent, aggressive, unkind, ungrateful and alcoholic cat, but he reveals his hidden light side of character as a father to Taco who almost died in action
Slash was at first hostile to Raphael and his brothers, but much later he reformed after Raph saves his life, even becoming leader of the Mighty Mutanimals.
Lori Loud is seen as bossy and stern sister, but despite this she's loving, caring and kind sister to Lincoln and her other siblings.
For the entire series, Eddy was greedy, rude and sarcastic person, but in the film Ed Edd n Eddy's Picture Show, he admits his brother is really a big jerk and that his scams aren't the best way to achieve friendship with others. As a result, he, Double D, and Ed gained acceptance among the Cul-De-Sac-Kids.
Manny was a grumpy mammoth, but after learning about his tragic past, his demeanor is changed thanks to Roshan, Sid and Diego.
Diego used to be part of the Saber-toothed cat pack led by Soto, but then later joins Manny and Sid on their adventures by defending them and Roshan from Soto.
For most of the time, Hanzo Hasashi/Scorpion was revengeful and ruthless revenant warrior servanting of Netherrealm, but after freed him he turn to good side of Earthrealm.
Chomper's Parents was hostile to Littlefoot and his friends, thinking they kidnapped Chomper, but much later after their son was saved from drowning and defeating Plated Sharptooth, they have become friendly towards the children.
Lapis Lazuli was initially hostile towards Steven and Crystal Gems in the episodes "Mirror Gem" and "Ocean Gem", but after Steven heals her in the latter episode she has become nice, lovely and friendly towards Steven and has made peace with the other Crystal Gems by the third season.
Peridot was introduced as an enemy of the Crystal Gems and a subordinate of Yellow Diamond, but in the months helping them stop The Cluster, she has outgrown the hierarchical and utilitarian mindset of the Gem Homeworld and has learned to appreciate the value of friendship, individuality, and life on Earth to the point where she defected to the Crystal Gems by the second season finale.
Lars Barriga started out as a jerk to Steven, but after being revived with Steven's tears, he becomes good and respectful to him, eventually becoming leader of the Off-Color Gems.
Pink Diamond was introduced as evil, cruel, ruthless and power-hungry as the rest of the Diamonds, but after noticing beautiful and peaceful life on Earth, she became a kind-hearted and caring guardian of Earth, leading Crystal Gems against Homeworld as Rose Quartz.
Bismuth started as ruthless and intimidating, but after Steven tells her the truth of Pink Diamond, she becomes kind and gentle as she joins Ruby and Sapphire's wedding and also becomes a permanent member of the Crystal Gems.
Blue and Yellow Diamond were introduced as ruthless and intimidating Gems longing to execute Rose Quartz and avenge Pink Diamond until they learned the truth that their sister and supposed murderer are one and the same.
Rexy at first was hostile to humans who invading the park, but later save them from Velociraptors.
Ashi started out being a hostile assassin to Samurai Jack, but she later becomes kind, lovely and friendly to him after he shows her the truth behind Aku's villainy.
Stay Puft was initially created as a Destructor Form for Gozer, but in the years following the evil god's demise, Stay Puft as "evolved" into a separate entity altogether. He has also as become a valuable ally to the Ghostbusters, helping them combat massive and ferocious ghosts such as Murray the Mantis and The Phantom.
Syren originally stole the youth of mortals and gave them to her evil sister Banshee as part of maintaining their happiness. But when Kylie Griffin revealed that she was merely a tool in her sister's schemes, she later turned on Banshee and returned the stolen youth before willingly surrendering to the Extreme Ghostbusters.
Turbo K.O. was created as K.O.'s uncontrolled rage and tried to destroy his own peers and Lakewood Plaza Turbo. But after he joined forces with K.O. to beat Shadowy Figure, he changed his attitude towards his heroic double and the two became good friends.
Homer Simpson begins Christmas with selfishness, and then realizes the error of his ways.
Wreck-It Ralph started out as a temperamental, brutish bad guy, but his friendship with Vanellope Von Schweetz allowed for him to transform into a compassionate hero.
King Triton used to hate humans, calling them barbarians, but his opinion changed when Prince Eric explained there is good in human after saving him from Ursula.
Garfield for most of the time he was a rude, lazy, hungry and unkind cat who bullied Odie out of jealousy, but revealing his good nature when he frees Odie from his cage and saves him from Happy Chapman.
Queen Elinor was a powerful queen who commanded the respect of everyone around her and was unable to connect with her daughter Merida until they learned to listen to each other and handle situations in a better way.
Shrek started off as a scary ogre who disliked intruders, but he let Donkey into his life and Princess Fiona into his heart, proving he is more of a teddy bear than a scary monster.
Eddie Valiant started out as a curmudgeon who disliked Toons with every fiber of his being since the murder of his brother, but then transcended that weight and became the Toons' hero by saving them from the evil Judge Doom.
For much of the series, Helga Pataki has been a total bully and was unfriendly towards Arnold and other people (including her sister Olga). While she hides her true feelings, her goals to overcome her hateful of Arnold by confesses him, but sometimes she getting along with Arnold. Until the second film The Jungle Movie, she was completely care for him, where her loyalty towards the football-headed boy in his mission to locate his missing parents opens his eyes to the depths of her feelings.
Cindy Vortex was Jimmy Neutron's arch-rival yet love interest in the film, Jimmy Neutron: Boy Genius and in the majority of The Adventures Of Jimmy Neutron Boy Genius until the episode "Lady Sings the News", when she completely becomes Jimmy Neutron's girlfriend.
Katherine Hillard started out as Rita Repulsa's servant, but later joins the Rangers as she takes Kimberly Ann Hart's place as the new Pink Ranger and becomes Tommy's new love interest.
Karone started out as Astronema, an enemy of the Space Rangers, but after being free from her brainwashing, she joins the Galaxy Rangers, taking Kendrix's place as the new Pink Galaxy Ranger.
Ryan Mitchell started out as an enemy to the Lightspeed Rangers after being summoned by Vypra but later joins the Lightspeed Rangers.
Hunter and Blake started out as enemies to the Wind Rangers, but after regaining their memories and working together alongside Shane, Tori and Dustin, they have become good as they join them.
Hi-Test was among a group of Mini-Cons genetically modified (and mindwiped) by Cyclonus' armada and was sent to steal Decepticon Hunters from Bumblebee's team as a means of freeing Soundwave from the Shadowzone. But after failing Soundwave, Hi-Test sought to right the atrocities he had made himself become a part of by helping Optimus Prime take down Laserbeak.
Cyberwarp was among a group of Decepticons masquerading as the Autobot High Council that plotted to bury the legacy of Optimus Prime and his Autobots, terrorize planet Earth, and restart the Decepticon Empire. However, believing that non-violent methods for reuniting Cybertronians could exist, she turned on her fellow Decepticons, allowing Ultra Bee to take down Galvatronus and restore order to their homeworld of Cybertron.
When woken up from centuries of stasis, the Guardian Knights attempted to attack Cade Yeager and Vivian Wembly for "stealing" the Staff of Merlin and execute Optimus Prime for betraying their people. But when Cade activated the Talisman's weapon mode Excalibur, they recognized the struggling inventor as the prophesized "Last Knight" and aided the Autobots and their human allies in halting Megatron and Quintessa's machinations.
Charlie B. Barkin started off as a conniving con man who was initially bent on using Anne-Marie in a scheme to get his money, but then grew to love and care for the girl, even saving her life.
Grumpy at first was rude to Snow White, since he disliked women probably because of the Queen's reign of terror, but then grew to be kind and helpful, and later, when Snow White was poisoned by the Evil Queen, he was the one who led the attack on the Queen.
Ivor was a vengeful maniac who created The feared Wither Storm in order for get revenge on The Order of The Stone, until he joined to Jesse to help defeat The Wither Storm.
The Undertaker was first seen to be mean and manipulative towards people, but after he turns Face, he becomes friendly, jovial and selfless person and he turned to the good side, then he married Michelle McCool, his wife.
Vegeta started out as an antagonist to the Z Warriors, but later turns to the good side.
Piccolo started out as an enemy to Goku before becoming his ally.
Yamcha started as an enemy to Goku and his friends before switching sides.
Tenshinhan started as an enemy to Goku and his friends before eventually switching to the good side.
Beerus was introduced as rude, selfish and destructival for the Earth, but he changed so long when he tasted earthling's food.
Catwoman started out as a villainess to Batman, but later becomes a heroine after Batman rescues her from Harley Quinn.
Shadow the Hedgehog started out as an enemy to Sonic before becoming the hedgehog's ally after remembering Maria's promise.
Tohru started as an enemy to Jackie Chan and company before becoming an ally to them later on.
Kane started as an hostile wrestler to his brother The Undertaker before becoming an ally to him later on to form the Brothers of Destruction.
Ian Hawke started as a greedy businessman, but later becomes an ally and friend to Dave Seville, the Chipmunks and the Chipettes after regaining his wealth and career.
Flash Thompson started as a bully to Peter Parker and the students including Gwen Stacy before becoming an ally to them later on.
Duncan used be a rude and unkind person but his friendships with Beth, DJ, Geoff, Owen and Zoey teach him well.
Blackarachnia started out as a member of the Predacons before eventually joining the Maximals in Beast Wars Season 3.
Penny Peterson used to be s spoiled, selfish and unkind girl who bullies Sherman out of jealousy, however she was kind-hearted and friendly to him as she redeems early.
Branch was a rude and pesimistic loner among trolls, but thanks to the positive influence from Poppy, his attitude has changed for the better and he became more open, nice and positive.
Enfys Nest initially acts like a cruel terrorist but later reveals herself to actually be a freedom fighter who wanted to use the coaxium for good.
Pacifica Northwest used to be a spoiled rich girl and a jerk to Dipper and Mabel, but later warms up to them and also becomes a love interest for Dipper and then she redeems herself.
Helios started as an cruel dragon who was responsable for capturing Tigrerra, but after he realizes that Drago is the Ultimate Bakugan, he becomes an friendly and valuable ally to Drago and their friends and helped them to battle the opponents such as King Zenoheld and Mag Mel aka Barodius.
Hydranoid started as an hostile Bakugan who was responsable for sending the Bakugans to the Doom Dimension, but after he betrays Hal-G, he becomes friendly and respectful dragon towards Drago and their friends and helped them to save New Vestroia and the Earth from disaster.
Bakugou Katsuki started from acting like a jerk to Izuku Midoriya for telling to him he's just a quirkless nerd who's not gonna be a real hero, but then he realized to understand Izuku's powers like All Might and they started to become friendlier-rivals.
Buttercup, being the "toughest fighter", has one moment of mischief, and another with innocence.
Mamá Imelda was bitter and strict, and banned music out of concern for her family. After singing "La Llorona", she reconciles with her husband Hector and lifts her ban on music.
Chloé Bourgeois started off as a mean rival of Marinette Dupain-Cheng throughout the first season of Miraculous: Tales of Ladybug & Cat Noir, but she changed her ways to become better in the middle of the second season, transforming herself into Queen Bee, and fighting alongside Ladybug. Also, she manages to win her mother's love after the latter was absent from the former's life for many years.
Lieutenant Penumbra caught Della Ducks on the moon, then later she turned when she questioned General Lunaris' plan to invade Earth,
Kevin Levin was evil and obsessed with besting Ben Tennyson at first, then later sacrificied himself to return Ben and Gwen to the present.
Vin Ethanol was introduced as an illegal racer, though he later joins the Tennyson family.
Despite his tough exterior, Tai is very often protective of his sister Kari.
Cartman is usually mischievous, but sometimes has a soft spot.
Ebenezer Scrooge is a very classic example of changing from greed to jollyness.
Kuzco changes from selfishness to friendliness.
Daffy Duck starts out as greedy, but redeems once he falls in love with Tina.
The Tod starts off as a greedy and selfish predator who only uses Rowf and Snitter to get food, but reveals that he has a strong relationship with the two dogs when he helps them escape the humans hunting them down.
The second Showa Godzilla started off as a villainous force of nature, but he later evolves into a defender of the earth and befriends other humans and monsters.
The Heisei Godzilla started off as a tragic and sympathetic being who is simply lost in human civilization and trying to survive, demolishing properties as a consequence, but he later evolves into an anti-hero who defends the earth from other evil monsters.