As Wanda possibly enters a "villain era" in Avengers: Age of Ultron. She then ed the Avengers as a heroine by the end of the film.
Marvel Comics has a history of characters jumping from villain to hero, many of whom made it into the MCU. Some have traded sides multiple times, some were villainized through misdirection to later be revealed as heroes by the end of a single film, and some were simply surviving. But each one has a robust redemption arc.
Valkyrie
Valkyrie had a heroic origin story based on Norse mythology, but after her entire squadron died in battle against Hela, she abandoned her life serving Asgard to be a scrapper on Sakaar. That's her villain era because she upholds the Grand Master's tyranny by capturing people like Thor and the Hulk to be enslaved.
Fortunately, Valkyrie finds herself disillusioned by the Grand Master's unfair gaming practices and her heroic core is finally awakened when Loki reminds her of her fallen squadron. It's only then that Valkyrie seeks vengeance from Hela, and helps Thor, Loki, and Bruce Banner defeat her.
Loki
Loki has had a complicated history throughout the MCU and was a major villain in multiple movies. He mind-controlled Clint Barton in Avengers: Infinity War.
But Loki never really wanted to hurt anyone, as fans learned in the streaming series, Thor: Ragnarok, Loki was able to find the company and attention he craves via heroic cooperation instead of destruction.
Bucky Barnes
James Buchanan "Bucky" Barnes is a complicated Marvel character. He starts off as a hero to one of the greatest Marvel heroes, Steve Rogers, but then goes on to be brainwashed into being one of the deadliest Hydra assassins of all time, the Winter Soldier.
Bucky's return to heroism from villainy is still an ongoing journey in the MCU. Some fans might have wanted him to take Captain America's shield at the end of characters like Sam Wilson's Captain America.
Black Widow Family
As the Infinity Saga in a long redemption arc. It started when she abandoned the Red Room and ed S.H.I.E.L.D., and ended with her sacrificing her life so that the Avengers could undo Thanos' Snap.
Her Red Room family in the Black Widow film mirrored her turn for good as well, inspired by her selflessness and leadership. None of them could have defeated Drakov on their own, and their heroic teamwork not only brought him down but also freed countless Black Widow assassins from their indentured servitude.
Gamora
After she was kidnapped by Thanos, Gamora had no choice but to become such a terrible villain that she was known as the "deadliest woman in the galaxy." But over time she was able to see the atrocities Thanos was committing and betrayed him.
Gamora's redemption arc is like a return to the good person she would have been without Thanos. She actually ends up as the moral core of her chosen family, the Guardians of the Galaxy, making her an especially great heroine.
Nebula
Fans meet Nebula as a truly menacing villain. She commits a lot of violent deeds and is called "the galaxy's biggest sadist" by a character named Tazerface, who is quite unsavory himself. She even betrays fan favorites Rocket and Groot to the Ravengers.
But Nebula's villainy is nothing more than Thanos' abusive programming. As soon as she is free, and experiences just a few moments of comion from Gamora and Tony Stark, Nebula becomes a vital hero with the Avengers and even kills her former self to save Gamora. Fans are hoping they will see more of her redemption arc in future.
Skrulls
The Skrulls are an oppressed race of shape-shifting space refugees, but because the viewers first meet them through the Machiavellian eyes of the Kree in Captain Marvel, they are painted as villains. But by the middle of the film, viewers, alongside Carol Danvers, realize that she has been manipulated by a merciless, militant civilization, and the Skrulls are actually their victims.
The Skrulls' plight as villainized victims acts as an apt analogy for oppressed peoples all around the world. Considering the conditions under which refugees are often subjected, their survival alone is quite heroic.
Trevor Slattery
Trevor's redemption arc is one of the most bizarre turns in the MCU. He is believed to be a powerful international terrorist in Iron Man 3. However, later in the movie, viewers learn that he is actually a squirrely out-of-work actor, who happens to appeal to the likes of actual villains.
His arc is better explored in Shang Chi and the Legend of the Ten Rings, as fans get to see Trevor working directly with the heroes, translating the vital directions of his mystical "chicken-pig" Morris.
Skurge
Skurge is an Asgardian warrior who had fought alongside Thor early in the MCU. When he returned in Thor: Ragnarok, Thor's blood-thirsty older sister Hela recruits Skurge as her villainous "executioner," the role she once played for Odin.
Despite being easily manipulated, Skurge has a strong redemption arc that revives his heroic warrior underpinnings. At a pivotal moment in the final battle, Skurge betrays Hela, fighting her reanimated soldiers, and sacrificing himself so that the Asgardians can escape.
Assorted Villains In What If... T'Challa Became Star Lord
In the universe-expanding animated series that explores alternate superhero timelines Black Panther. In this alternate universe, heinous galactic villains like Nebula, the Ravagers, Korath, and even Thanos are inspired to be heroes instead of villains.
The episode explores the theme of individual nature versus environmental nature, contending that T'Challa's heroic and virtuous core transformed the role of Star-Lord from Ravager scoundrel to the strong moral com the galaxy desperately needed.
