Twin Desynch

Say you have an Evil Twin. Pretty bad, huh? There's always the possibility he might attempt to pull a Twin Switch and blame you for god knows what villainy and force you to go tell your teammates "Clear My Name".

But sometimes, that's gladly out of the question. Back when he was just The Rival you two used to look a lot alike, but since he had his Face Heel Turn and you both went Cain and Abel on each other, he changed his physical appearance and now people just wouldn't be able to confuse you both. This is symbolic for how two people that would normally be pretty much the same have gone in vastly different ways in life and it shows. Also It represents how the twins have officially stopped thinking like each other.

Compare Important Haircut and Evil Costume Switch.

Anime and Manga

 * In Trigun, Vash and Knives didn't really start to hate each other until.
 * Though honestly Vash seems to blame Knives less for the arm than for the fact that he psychic-hacked his other arm to blow up a city full of people (not that he hadn't already crossed the Moral Event Horizon) and Knives is mad that Vash pointed the giant gun straight at Knives when he couldn't stop it from firing, apparently blowing off half his body—he evidently spent several decades growing it back.
 * And Knives had already attempted genocide (killing their mother figure in the process) and Vash had already denied and shot Knives by this point and was somewhat planning to kill him; this just confirmed them in their roles. Besides, the anime versions always looked kind of different. Paler hair and bluer eyes for Knives.
 * Much earlier, in the anime, one of the early pieces of Foreshadowing of Knives' eventual Face Heel Turn (like we needed it) was when he cut his hair in a different style from Vash's when they were about a year old, in a dramatic scene in a dark room. And said, "if we stay the same we'll have no individuality."
 * One story in ×××HOLiC featurs a pair of identical twin sisters, one of whom suffers from a crippling lack of confidence, especially when comparing herself to her much more vivacious sister. After Yuuko helps her overcome her issues, her price is the girl's long hair. The girl happily complies, saying that her new look is another step towards removing herself from her sister's shadow and pursuing her own personality.
 * Inverted in Eyeshield 21. Throughout the entire series, the Kongo twins were nothing alike and didn't seem very close. Not only were they opposites in personality, but Agon had a long man of dreads. Towards then end of the series Agon's head is shaved bald and he purposely shows it off as a sign of camaraderie towards his brother.

Comic Books

 * Judge Dredd: Joe Dredd and Rico Dredd were clone-brothers, and thus theoretically looked identical at first (Joe being The Faceless.) But by the time we actually meet Rico, he's undergone massive facial cyborging to survive his prison sentence on Titan.
 * Played with in Yoko Tsuno. Khany and Poky were young twins when they were placed into suspended animation. They were awoken at different dates, resulting Khany being an adult and Poky remaining a child.

Film

 * Evil Dead: Evil Ash gradually becomes a monstrous Undead.
 * Captain Picard and Praetor Shinzon in Star Trek: Nemesis are like this. As a clone created more recently, and suffering from an illness that causes (awesome-looking) Glamour Failure, and having been injured and improperly healed several times, Shinzon looks very little like Picard does, and probably wouldn't be an exact match for Picard at 20. The idea of impersonation, etc. never comes up. A villain who wasn't a clone of Picard could've worked nearly as well - except for the part where he needs Picard alive in order to cure himself, and what he represents - had his life gone differently, Picard could perhaps have been just as evil For Want of a Nail. Picard tells him that the reverse is true, and that Shinzon has equal potential for good. (Shinzon stays a bad guy anyway, though.)

Literature

 * In the Robert Heinlein juvenile novel Time for the Stars after the more easygoing twin discovers his more dominant brother manipulated him into going on the interplanetary voyage in his place. (Relativity plays a hand in it as well.)
 * Caramon and Raistlin Majere from the Dragonlance books. To be honest, they were pretty different when the story started, but not so much before a certain traumatic event. Caramon has always been bigger and stronger, though. Also, during the story, their differences grow even more.
 * Occasionally, though, they happened to have a very similar facial expression. In those cases, there was always a third party character pointing out how much they look like and how foolish he/she was, not having seen that earlier.

Tabletop Games

 * In Ravenloft, the wererat darklord Jacqueline Renier deliberately imposed this trope on her identical twin Louise, ripping her earlobe in a family fight. A variant in which both twins are pure evil, and the desynch illustrates one of them rising to dominance rather than having a Face Heel Turn.

Video Games

 * Dante and Vergil had a somewhat heated rivalry in Devil May Cry 3 but still felt somewhat guilty about it. That game was a prequel to its predecessor, Devil May Cry, where they really stopped pulling the punches and.
 * May not count, since DMC1 Dante didn't know it was  until after the final battle. Although the player might have guessed, what with the hints and all.
 * In Metal Gear Solid, Liquid Snake went from just another megalomaniac with a nuclear tank to Snake's Arch Enemy once he performed a Grand Theft Me on The Dragon, Ocelot. Subverted because.
 * Also, they started out life looking identical (both being clones of Big Boss) and received near-identical upbringings (one in the US military, one in the British). However, sometime after they split up as children, Liquid became a megalomaniac, dyed his hair blonde, grew it out, and stopped wearing a shirt. Solid sticks with the "brown mullet, spysuit, and professional terrorist and conspiracist fighter" motif daddy used back when he was a Snake.
 * The cause and the consequence are switched around in Higurashi no Naku Koro ni, were Shion started to resent Mion when she received the tattoo that branded her as the leader of the Sonozaki house. Specially painful seeing how.
 * In Mother 3 this is subverted as.
 * Warcraft: Malfurion and Illidan Stormrage. Though they weren't identical twins to begin with (they had at least different hair colors), Illidan lost his eyes and got glowing tattoos with his first Deal with the Devil, and bat wings, horns and furred legs with hooved feet when he absorbed the power of an evil artifact. Malfurion looked like a relatively normal night elf for a while (with the exception of stag antlers), but he has now gained other animal traits, like bear paws and bird wings.
 * Porom in Final Fantasy IV: The After Years now has a Stripperific outfit and pink hair, unlike her brother Palom who pretty much looks like in the original game but taller. They had a very heated discussion after Palom decided to move from their village and become a sage like Tellah.
 * No More Heroes

Web Comics

 * Melonpool has both Ralph Zinobop and his nice clone Ralphie as main characters. Though physically identical, Steve Troop draws them with such different expressions and body language that it's almost always easy to tell who's who.

Western Animation

 * Parodied on Futurama; The Professor's clone doesn't look like him because he was kept in a test tube too long and his face was mashed against the glass.
 * That's sort of a moot point here, as there's an approximate age difference of 148 years between them.
 * Totally Spies!: Jerry's brother, Terry, went through plastic surgery to make himself absolutely incomparable to Jerry. This is all for placing the blame on him for cheating and making him repeat the Second grade
 * In All Grown Up!, Lil gets upset that everyone things of her and her brother, Phil, as just part of a matching set. By the end of that episode and in subsequent ones they start dressing differently to stand out from each other more.

Real Life

 * A Truth in Television semi-example would be Benji and Joel Madden of the band Good Charlotte. While not a matter of good and evil, they are identical twins who go out of their way to look nothing alike.