Villains' Absolution

Villains' Absolution is the trope/phenomenon describing that some villains give up their evil ways to become good.

This event is essentially a form Heel-Face Turn scenario where a villain decided to become a good guy, though in the case of Villains' Absolution, the wrongdoer would reflect the error in their ways and sees that in spite of how far he/she go in the path of evil, he/she realized that he/she still have the chance to return to the good side.

There are several ways a villain can redeem themselves including: IMPORTANT: If the villain is currently in an On & Off status, do not add them unless they stayed good right up to the very end of the story. Also, do not include villains who have done a few honorable/heroic actions, then gone back to their villainous ways afterwards. Additionally, Pure Evil villains have no chance of any redemption, no matter the circumstances. Likewise, it is impossible for a redeemed villain to revert back to their evil ways unless they are brainwashed by another villain (or villains).
 * Snapping out of a possessed or brainwashed state, and deciding to aid the hero who freed them. The villain is a hypnotized, brainwashed or possessed pawn who does not know they are being controlled until they are freed. Grateful to whatever hero freed them, they ally with them. The cyber ninja Cyrax and the lost Edenian queen Sindel from the Mortal Kombat universe are the examples.
 * Being exposed to a messiah or pure of heart type of hero who helps them see their errors. Usually done with delusional, honorable, or insecure villains (the wrongdoer can also have all those traits) who believe they are doing right or just want to be loved. The hero reveals to them that their actions are actually causing harm, or tries to comfort them. The individual chooses their desire for righteousness over what they have done, and/or decides the hero had helped them see what they were doing was wrong, and becomes a hero. Prince Zuko is an example.
 * Choosing honor before evil. An honorable villain decides that their own honor, or the honor of something or someone else, is more important then what they are doing and decide to abandon their evil actions. Often done with supporting antagonists who value the lives of lower-ranking people in an organization such as Boss Wolf.
 * Becoming friends with someone and decide to help them over being evil, such as Axel who had planned on betraying Organization XIII with Saïx, but over time built a friendship with two other members, Roxas and Xion, and decided he was happier being with them rather than plotting with Saix.
 * Choosing their family over evil. Done with villains who have families and to care for them. They realize that their actions are actually hurting their spouses, children, siblings, or any other relatives in their family. One example is Darth Vader.
 * Being memory-wiped or brainwashed into becoming a hero and deciding that they like their new personality and life better then their old one when they inevitably learn the truth. This is the rarest and most controversial form of a villain redeeming themselves since they did not turn good by their own free will and essentially had to be programmed into being good. Reserved only for villains who would normally be Pure Evil under their circumstances, the audience or reader meets them as a hero first, not knowing they are brainwashed or have fake memories. The "hero" does not know this either and is just as horrified as the viewer when they learn the truth about the horrible things they have done or regain their real memories, but they have spent so much time as a hero and living with an artificial good personality that they choose their new life over their former one and become true heroes. This also includes individuals that happened to be robotic villains that were meant/programmed to be the Big Bad's trump card against the heroes, but due to a certain incident, it ended up discovered and fixed by the heroes that he/she meant to destroy. The said individual even later befriended the said heroes without either them or said individual aware with his/her true goal. One famous example is Darth Revan. Another is Professor Pericles; although he did turn good, it was only in an alternate reality and didn't do out of the goodness of his own heart.
 * Betrayed by their fellow villainous allies/bosses, which made them choose to turn to the good side. After they antagonize the hero and their deed succeeds, their allies/bosses dump them or try to kill them straight away; either way, the said villain escapes. Having seen the error of their ways (and in the worst case, hunted down by the big bad or their former ally which left them no option but to join the heroes to survive), they choose to turn to the good side by joining forces with heroes. Discord is an example.
 * Retiring from being a villain and realizing that living as a good guy is more better than his previous life as evil-doers. Megamind and Professor Badlam are good examples.
 * Learning the lesson of being evil from other villain (usually a Necessary Evil, a Monger or, in the worst of cases, a Pure Evil) In other words, they experience a case of "getting a taste of your own medicine," which leads them to understand that what they are doing is very bad and they feel horrified, disgusted and terribly bad for the actions of the latter villain and try to redeem himself/herself and fight against him/her (a similar but somewhat different to a case of Evil Vs. Evil). In the end of the battle (usually in the end of the very battle/episode/movie or in sequels), he or she will try to join the heroes and search for the pardon to everyone they had become enemies. Shadow the Hedgehog, Lucy, and Selina are good examples.
 * Simply stopping being evil: There are rare cases where, though they have no real reason, a villain can just decide to stop being evil. Perhaps they tire of it or have successfully completed their goals and have no reason to antagonize anyone anymore. Some of these villains may not be remorseful like other redeemed villains, and instead are proud of what they have done but simply have "retired" from villainy. A good example is the Hatbox Ghost.

Cartoons, Manga and Anime

 * My Little Pony:
 * Nightmare Moon: Twilight Sparkle and her best friends used the Elements of Harmony to transform Nightmare Moon back into Princess Luna.
 * Starlight Glimmer: Twilight Sparkle brought Starlight Glimmer into the terrible future after another failed attempt to restore the past, but Starlight was persuasive for cutie marks costed Starlight her only friendship. So Twilight offered Starlight her friendship.
 * Sunset Shimmer: After Twilight Sparkle and her human world friends used the elements in them to defeat Sunset Shimmer, changed back from a demon into normal, she immediantly shed tears and apologizes for her actions. Later, Sunset Shimmer implored the human Twilight Sparkle to do the same after the latter's freak accident that turned her into violent and destructive being called Midnight Sparkle.
 * Chirn: As soon Chirin invaded his childhood farm, he saw a lamb that was like him when he was young and his mother saving him. He then had some second thoughts, but the wolf did had the same beliefs, so Chirin stopped him, saving the sheep for he remembered he's the wolf who killed his mother. Sadly, in spite of his redemption, Chirin's training that resulting his transformation into a monstrous being that he became has condemned into a half-life for the rest of his life (his childhood farm inhabitants exiled him for how monstrous he had become).
 * Terra: After the Teen Titans revealed to survive her attacks, Slade revealed his true color by abused her and even showed lack of concern with her well-being, pressured her enough to went against him.
 * Jinx: Kid Flash charmed her saying, she does not have to be the bad guy.
 * Dark Heart: When Dark Heart was attacking the Care Bears, he hit Christy as well, and he started to feel remorse since she save him from drowning.
 * The Grinch: His in How the Grinch Stole Christmas is no doubt one of the most famous absolution in history. After the Whos in Who-Ville sang without the presents, he began to realize that Christmas isn't about presents with the guilt for his evil act hurt him so much that it feels as if his heart become larger.
 * And in The Grinch Grinches the Cat in the Hat, the Cat in the Hat along with the other troubled people reminds the Grinch about his mother, and then starts feeling remorseful.
 * Prince Zuko: After some time in the fire palace and learned that how Fire Nation become monstrous forces revealed to be rooted from Sozin's betrayal against Avatar Roku (whom later reincarnated into Aang), Zuko realizes that he should join the Avatar gang, though he succeed to gain their trust once he aid Katara to confront her mother's killer.
 * Mai and Ty Lee: Mai went against Azula for the love of Zuko and Ty Lee went against Azula for Mai, inadvertly exposed the fact that whatever bond that they share with Azula all this time was fake.
 * Kraehe: Kraehe took a glimpse of her past and discovers who she really is: not the daughter of the Raven, but an ordinary girl. With that she lost her Kraehe side and permanently stayed as Rue for good.
 * Lord Business: Finn tells Business that people's creativeness are wonderful, he's one of the greatest people who ever lived and he does not have to be the bad guy whom limited everyone's creativeness.
 * Iago: In The Return of Jafar, Iago got fed up with Jafar's abuse and joins the good guys for his own gain, and eventually stars to actually warm up to them, and eventually redeems himself by kicking Jafar's black lamp into molten lava, destroying him forever.
 * Carface: In An All Dogs Christmas Carol, after the visits of Charlie, Itchy and Sasha, Carface sees the errors of his ways and decides to stop Belladonna.
 * Scalawag and Igor: After Pinocchio saves Scalawag and Igor from the Pike, they start to have second thoughts about selling him to Puppetino and the Emperor of the Night.
 * Peridot: In Steven Universe episode "Message Received", she joins the Crystal Gems by insulting Yellow Diamond and calling her "clod" after refused to destroy the Earth with the Cluster.
 * Bismuth: In Steven Universe episode, "Made of Honor", she joins Ruby and Sapphire's wedding after discovering the truth of Pink Diamond and also becomes a permanent member of the Crystal Gems.
 * Janja: Becomes surprised when Jasiri saved from certain death, leaving him hesitant when she then asked him to join despite his refusal but leaving her sure he will come through.

Live-Action Movies

 * Darth Vader: His is no doubt one of the most famous absolutions in history. When his son, Luke Skywalker was being tortured by Emperor Palpatine, Darth Vader sacrificed himself to save Luke by throwing Palpatine into the pit. As he was dying, Vader asked Luke to remove his mask so he can see his face for the first and the last time.
 * Winter Soldier: Having this once he remembered his past self and saved Steve Rogers from drowning, and set out to destroy HYDRA's assets that used to brainwash him. Unfortunately, returned to the good side by his own terms is not enough to retain his good self due to HYDRA has arranged a fail-safe programming in his brainwash procedure where he would revert to his brainwashed self for limited amount of time via trigger words.

Literature

 * Ebenezer Scrooge: His' no doubt one of the most famous absolutions in history. After the visits from the first two spirits and seen what the Ghost of Christmas Yet to Come shown what will his future be like, Scrooge apologizes for all the wrong he did and he will change and honor Christmas in his heart for the rest of his life.
 * The Once-Ler: The Once-Ler realizes the errors of his ways (a little too late) when he chops down the last Truffula Tree of them all.