Some of the Gym Leaders and Elite Four members in Pokémon. While most of them (with the exception of Giovanni) are good guys in the games - Lance and Lorelei even helping out the player character at key points - Lt. Surge, Koga, Sabrina, Agatha, Bruno, Lorelei, Lance, Karen, Will and Pryce became villains in the manga adaptation Pokémon Special. To be fair, though, Pryce is a more sympathetic Anti-Villain, Lance is a Well-Intentioned Extremist, and most of the other characters listed reform later on, with the exception of Agatha.
This is utilized to a lesser extent with their anime counterparts. Sabrina is converted into something of a demonic witch who antagonizes Ash and co., while many others, most notably Lt. Surge, Erika, and Skyla, are egotistical Jerkasses with a condescending demeanor towards their challengers (or, in Erika's case, towards those who don't appreciate the perfume her gym makes). All of them make friends with the heroes in the end. However, others, like Brock, Misty, Cilan, Iris, and Clemont, join Ash as protagonists and are more openly heroic characters.
Pokémon Special has a downplayed example with Norman. In the games, Norman is a kind, gentle person who respects his child's wishes and would most likely not use physical violence. In the manga, Norman is a lot meaner and beats up his son for disobeying him. Despite his harshness, he is on the side of good - he is genuinely supportive of Ruby.
In Pokémon Black and White, N is a very sympathetic Anti-Villain with good intentions. He eventually makes a Heel-Face Turn in the sequel games, helping the player against Ghetsis, his much more evil adoptive father. However, in Pokémon Special, N has fewer redeeming qualities and manages to convince White's Tepig to leave her. His goal also seems to be more like Ghetsis' goal than in the games.
In Pokémon Black 2 and White 2, Colress, while still a scientist in the employ of Team Plasma, does encourage the player and even gives them a device needed to progress further in the game. He is involved with Team Plasma For Science! and is not particularly interested in their goals, expressing distaste for Ghetsis. After his defeat, he encourages the player to stop Ghetsis' plans. In Pokémon Best Wishes 2 Episode N, Colress is a true Mad Scientist who experiments on Pokémon to the point of torture, uses mind control on the Pokémon in his introductory episode (including those of the main characters), and is more than willing to hurt Ash and his friends to prove his theories. He is also more appreciative of Ghetsis due to Plasma's "providing" increasingly more difficult "subjects" pushing the theories further. Colress in the game has a Heel-Face Turn, willingly disbands Team Plasma, and becomes The Atoner after Ghetsis is defeated, while his anime counterpart is arrested by Looker. The Anime counterpart does come up with the idea for a Pokemon translator, but after he's arrested and in a way emphasising his Blue and Orange Morality.
The Pokémon Special version of Colress is portrayed along the same lines as in the anime.
Gendo Ikari: In the anime, he is Ambiguously Evil, he sincerely praises Shinji for his combat performance at one occasion, and with his Famous Last Words he regrets having been a bad father to him. In the manga adaptation, he is unquestionably evil, has a massiveGod-complex, and outright hates Shinji. In the manga, he's also implied to have personally killed Kaji, whereas it was unknown if he had anything to do with it in the anime, even though he was hinted at being involved somehow. He's somehow even worse in Campus Apocalypse.
In the Mai-HiME manga, the main antagonists of the first arc are Haruka and Yukino, the latter of whom is friends with Mai and Mikoto in the anime, and the otherwise heroic Akira assists them. By contrast, Shizuru never turns Psycho Lesbian, and Nao (reluctantly) helps the heroes after the teams merge.
The 2003 Fullmetal Alchemist anime has several cases that were due to those characters not having been well established yet in the manga when the anime overtook it. Basque Grand was transformed from a Reasonable Authority Figure and Colonel Badass into a Colonel Kilgore and General Ripper who just can't wait to commit some more genocide. Kimblee, while an awful person in the manga, had his negative qualities cranked Up to Eleven, and his good ones suppressed. Even Hohenheim, the Big Good in the manga, became a Retired Monster; instead of being tricked into helping Father turn the nation of Xerxes into a Philosopher's stone, and only becoming aware of the plan once it was too late to stop it, he and Dante turned people into Philosopher's Stones to prolong their lives.
Wrath and Envy were already horrible monsters in the manga, but the anime made them worse. Wrath (now named Pride) loses all of his Noble Demon qualities and his last scene involves him strangling his Morality Pet, Envy had his sadism cranked to maximum, and both lose their Alas, Poor Villain moments.
In a similar but lesser manner, Shadow the Hedgehog in the Sonic X anime. In the games, Shadow started off a vengeful weapon ready to destroy Earth's population in honor of his murdered friend. Throughout his story however, he is portrayed with a palpable sense of doubt and emotional conflict, before ultimately pulling a full Heel-Face Turn two games later. In the anime, he roughly follows his games counterpart's story, but maintains his more sinister neutral alliance and is The Unfettered to the highest scale (at least once perfectly willing to kill a child in cold blood, along with anyone who defended her, if it meant stopping a Bigger Bad).
Black Widow and Hawkeye are usually depicted in both the 616 and Ultimate universes as Anti-Hero allies of SHIELD. The MovieRise Of The Technovore depicts them as much more antagonistic and villainous.
In the manga of Deadman Wonderland, the staff of the titular prison Hand Wave the prisoner deaths in the dog races by claiming that they are done with special effects. In the anime, the special effects angle is done away with; and the prison openly admits that many of the competitors do not survive and die brutal deaths.
Kaede Fuyou from SHUFFLE!. While not exactly a villainess, she did, in both versions, believe that Rin was responsible for her mother's death (a misconception he encouraged to prevent her from losing the will to live), and abused him for years until learning the truth, at which point she devoted herself to him in order to atone. In the anime, in which Rin canonically goes out with their mutual friend and senpai, Asa, resulting in him spending less time with Kaede (in part not wanting her to be consumed with him), she snaps and attacks Asa, causing her to collapse, but comes to regret this later. In the visual novel, after finding out that Rin and Asa are a couple, Asa apologizes, but Kaede sadly accepts their relationship, albeit with the scene being somewhat similar to Kaede and Asa's reconciliation from the anime.
The Dark World Fiends were presented as villains in the third season of Yu-Gi-Oh! GX, which contradicts the flavor text of some of their cards in the game and the Master Guide 2, which claims they are not evil. In fact, the flavor text on Zure, Knight of Dark World's card claims that he "never oppresses the commoners", while that's probably what he's most notorious for doing in the anime.
Also, in the manga version, Jim Cook is an antagonist who is far more malicious than his lighthearted and benign anime counterpart. It's not his fault, however; he's a Brainwashed and Crazy pawn of Tragoedia.
In the manga version of Yu-Gi-Oh! 5Ds, pretty much every character has a different background and personality, but Rua and Ruka more so than any other. They start of as villains in this version (and rather sadistic ones at that) very unlike the kind and innocent children they are in the anime. It is later revealed that Rua underwent a Duel Dragon ceremony to save Ruka from an illness, only Luna to become enslaved by the spirit of one of the Duel Dragons and for Rua to become Brainwashed by her. Eventually, Yusei is able to use his more benevolent Dragon to break the spell.
In the manga version of Chrono Crusade, Big Bad Aion is portrayed as misguided and possibly insane, but sympathetic, having turned to evil deeds in a desperate attempt to fix what he felt was a corrupted system after learning an Awful Truth. In the anime, he was turned into the literal Anti Christ.
Prétear: In the manga version, one of the Leafe Knights ( Sasame, the Knight of Sound) is strongly hinted to have been in love with the villain in the backstory, but he's definitively a good guy and remains that way for the entire story. In the anime, where Fenrir plays a bigger role, he eventually breaks down and becomes her minion because of his Mad Love.
Queen Beryl of Sailor Moon was a villain in the manga, but an ultimately tragic figure who was manipulated by Metaria into her crimes in her past and current incarnations, and ultimately doomed not by her villainy, but her own belief that she was beyond redemption at this point. In The Ninetiesanime, she's a straight-up evil villain who willingly and loyally serves Metalia.
The first anime of Black Butler does this with Queen Victoria, of all people. In the manga she's a straight Cool Old Lady though she seems to like the idea of a Zombie army, while in the anime she's responsible for Ciel's parents' deaths, and planning to start a world war to "cleanse" the world with her angelic accomplice, Ash.
The Cheshire Cat in the manga adaptation of the Kingdom Hearts series is outright villainous, compared to his more neutral role in his origin book and in the game. Maleficent even offered him a place in her group, but he declined.
An odd example comes with Anchovy, since the manga was released before the anime showed her match with Oarai. In the anime, Anchovy's competitive but fairly good-spirited, and after losing, invites the Oarai crew to eat with her and the people who set up the match. In the manga, she starts off by accusing Miho of having a "weak" way of tankery, and at the end, accuses Miho of costing her old school the championship by abandoning the flag tank.
Erika is a Jerkass in the anime, but mainly to the extent of being snide and condescending toward Miho (for example, in the finals, saying that Oarai must be weak if she became its commander). In the manga, between the semifinals and the finals, Erika flies over to Oarai, confronts Miho, and angrily accuses her of not just costing them the victory, but abandoning them in their time of crisis, and vaguely insinuates that Miho traded her vice-captaincy of her old school for captaincy of her new school. She's significantly more vicious and angry in that scene from the manga, and leaves Miho in tears at the end of it.
In the Bokurano manga, Koyemshi/Dung Beetle is quite a jerk throughout, but he has a few Pet the Dog moments, such as performing a Mercy Kill on his sister, Youko, and giving Ushiro reasons to fight. In the anime, he's significantly more vicious, including mocking one of the dead kids, was quite a Dirty Cowardwhile he was a human and ultimatel gets killed by his aforementioned sister when he tries to force the youngest of the group into the game.
InuYasha: Izumo/Gyu-oh of episodes 94 and 95. The English dub of those episodes makes him a full-fledged villain, whereas the original Japanese made it clear that he was a Tragic Monster who was just driven by his madness.