Single-Minded Twins



""Are you thinking what I'm thinking?"

"When aren't I thinking what you're thinking?""

- Gemma and Gem, Power Rangers RPM

""They look so god-damn like the same person, I would say to them 'You want ice cream cone?', both of them say yes!""

- Group X, "Mario Twins"

Sometimes a writer wants to include twins as characters but doesn't want to give them different personalities. They're just "the twins", for the most part, and even though they might have different first names, they're essentially the same character. The twins aren't really the Creepy Twins or users of Twin Telepathy; they're written just one character in two separate bodies and have only one personality between the two of them. There's no real difference between the two, and they're generally presented as one consciousness split between two bodies and are never apart.

The opposite of Different As Night and Day. If they're on a superhero or villain team of some sort, they'll often be counted as a "single" member (like the Witches 5 from Sailor Moon - which was actually six girls, but two of them were twins). Particularly weird when they're Half Identical Twins.

Real twins usually cringe when they see this trope anywhere, seeing as how most of them dislike having their individuality marginalized, and even go so far as using Identical Twin ID Tags.

A subtrope of The Dividual. Compare Those Two Guys. Often overlaps with Heterosexual Life Partners.

Anime/Manga
""I'll be Gretel for a while, now.""
 * As mentioned above, Ptilol and Cyprine from Sailor Moon, who were really one person in two bodies. In the French dub, they refers as each other doubles, and their names are Émilie and Émilia.
 * Up until they can't agree on how to kill someone, anyway.
 * There's also a pair of youma under Nephrite who have different powers--dark reflections of Mercury's and Mars'--but otherwise look nearly identical except for color and act as one until they have a spat (over which is doing more to kill the senshi) which gives the soldiers the in they need and the audience a ham-fisted sermon about cooperation.
 * Despite so little screentime, Phobos/Deimos, Lethe/Mnemosyne, and Chi/Phi might be like this. Chi and Phi seem to be one-minded in wanting to kill the senshi, anyway.
 * Pyun and Potaro from Dai Mahou Touge.
 * Jougan and Barinbou, the twin Big Guys from Tengen Toppa Gurren Lagann. They are never seen apart from each other, and while they don't finish each other's sentences, they often do split a complete statement between them, with one taking one full sentence and the other taking the next.
 * Imari and Sayoka from Inukami
 * Subverted in Ouran High School Host Club with identical twins Hikaru and Kaoru: they start out following this trope to a tee, speaking together and Finishing Each Others Sentences, but by the middle of the series they've developed entirely distinct personalities... and Kaoru even recognizes that this trope is unhealthy and takes steps to try and avoid it.
 * Even before that, it was established early on that Kaoru was passive while his brother was aggressive, both on and off their Host Club "stage." Later on it's revealed that they put on an imitation of this trope to drive people away outside of school. When Haruhi manages to see through this act, they start loosening up, to the point where their true personalities begin to surface.
 * They're a little surprised by how many differences they actually have; they tended to think of themselves this way a lot of the time, especially after the only babysitter they ever liked turned out to be an infiltrator and reinforced their preference for distrusting everyone who wasn't them. Panic is had on Hikaru's side when he realizes there is a gap forming down the middle of their 'us.'
 * They did the 'falling in love with the same girl' thing, and their different reactions to the dilemma set off the division storyline. Basically, Kaoru is naturally more mature, and winds up taking care of Hikaru in this regard.
 * Emi and Yumi in Irresponsible Captain Tylor.
 * Ai and Ren from Kanokon
 * The Autobot Clones and Decepticon Clones in Transformers Headmasters.
 * Hansel and Gretel from Black Lagoon. Sure they are presented as slightly different personalities, with different genders, until they switch the gender and accompanying personality between them.


 * Yu Fang and Yu Lan from Full Metal Panic. Though they do split up every now and then for certain missions. However, they appear to have pretty much the same personality.
 * Not at all, Yu Lan is the slightly shorter, short haired, short tempered, and short-spoken younger sister who specializes in hand to hand, short range combat. Yu Fan has longer hair, is a little taller, is a trained AS pilot and exhibits a more normal personality and is called "Oneechan" by Lan. Even tough they are twins, they obviously took on different roles.
 * Ranma One Half has two sets of Single Minded Twins; one unique to the anime, one to the manga. The anime has Ling-Ling & Lung-Lung, who aren't identical twins (with different hair colours, eye colours, weapons and hair styles), but nevertheless act as functionally one person. The manga has Pink & Link, who act like this when they come to Nerima, but are portrayed as being Different As Night and Day in their backstory.
 * The first movie, Big Trouble in Nekonron, China, has the Lucky Gods Daikokusei and Daihakusei, two Go-playing siblings who are functionally identical. The only difference between them is that one plays white and the other plays black.
 * Jasdero & Devit from ~D.Gray-Man~. Literally.
 * They even do a fusion thing where they fight as 'Jasdevi;' this troper took a while to learn their individual names.
 * The second season of The Slayers has a pair of these; identical twin martial artists who want to be famous pop idols and who get into a fight over what Lina thinks is a book of spells, but turns out to be a collection of lost folk remedies. For added measure, Mimi and Nene are physically identical to Ranma One Half's Shampoo.
 * The Tachibana twins, Masao and Kazuo, in Captain Tsubasa. They're also Genre Savvy to the point of using their single-mindness as a game strategy.
 * The Twin card from Cardcaptor Sakura. They move in perfect symmetrical unison and can only be sealed after being beaten simultaneously, as they're pretty much just two halves of a single entity.
 * In the increasingly-weird later novels based on the Doom games, the main characters encounter a member of a species of aliens that look vaguely like upright-walking gorillas and are born as Single Minded Twins. They choose the name, for ease of use of the humans, "Sears & Roebuck".
 * Mei and Kyū (Para and Dox in the dub) in ~Yu-Gi-Oh!~.
 * They had NAMES?!
 * Mairu and Kururi, 's younger sisters in Durarara! -- Though they outwardly act as Different As Night and Day. Playing with the trope a bit, the twins' single-mindedness is an indicator of how unhinged and detached from reality growing up with  has made them.
 * Houzuki and Bonbori from Otome Youkai Zakuro. They're good natured and see Hanakiri Ganryuu as a playtoy, but they are also half-spirit. Good idea not to mess with them.
 * In Saiyuki, Gonou seems to have believed this about himself and his Half Identical Twin sister, which in his mind justified their relationship. Subverted in that they were canonically matching-but-opposite personalities, and it's presented as unhealthy.
 * Literal case in Claymore. They were train/build that way too.
 * In Magical Girl Lyrical Nanoha Vi Vid, Dieci notes that the first time the twin Combat Cyborgs Otto and Deed have disagreed on anything is whether Corona or Lio will do better in the tournament. This disagreement is presumably because the twins each trained one of the girls, and thus chose to favor the one they trained.
 * In the anime version of Trigun this trope is referenced by the young Knives: once positively, with regard to one of them being bullied, and once negatively, after he gives himself a haircut: "if we stay the same, we won't have any individuality."
 * Of course, they then spend over a century Different As Night and Day.
 * Souya and Shirase from Mawaru Penguindrum.

Comedy

 * Bob and Ray had a pair of recurring characters named Clyde and Claude McBeeBee, non-identical twin bandleaders who went everywhere together and always spoke in unison.
 * One comedienne specifically cites and mocks this trope. "I have a twin brother. People are always asking me things like, 'You're twins; can you hear each other's thoughts an' stuff?' 'Yeah. Oh, hang on...he thinks you're an idiot.' "

Comic Books

 * Ladyhawk, a supporting character(s) in Spider-Girl, is/are a set of twins sharing the same superhero name and identity (so they can operate at full-time for a single hero while still maintaining private lives). They are implied to have distinct personalities, but since their screen-time is so limited, the only observable difference is that one of them is more experienced.
 * Now that, they seem to have become more like Yin Yang Twins.
 * The Stepford Cuckoos (Celeste, Esme, Mindee, Phoebe, and Sophie) in the X-Men family of books, are identical quintuplets and form a "Five-in-One" telepathic mind.
 * Though never explicitly stated (it's implied to be the result of a string of freak coincidences), Batman villains the Trigger twins. They first met when they both attempted to rob the same bank, only to discover their exact resemblance to one another. Ever since, neither of them has ever seemed to come up with an idea the other hadn't been thinking of as well.
 * The Thompson Twins in Tintin, who are not technically twins but are virtually indistinguishable - the only difference is their moustaches. Furthermore, in the original French, they were known as Dupont & Dupond, which are even pronounced identically - this was kept up at least to some extent in most translations, including English, where they are known as Thompson and Thomson.
 * In standard English Thompson and Thomson are pronounced identically as well, by anyone who isn't consciously trying to demonstrate how they pronounce them differently.
 * Ken & Kyle Katayanagi, the 5 and 6 evil exes of Ramona, from Scott Pilgrim. While we can't see much of them through volume 5, as they usually send robots to attack Scott, they pretty much seem to think and talk at the same range, finishing each others sentences at times.

Fan Fiction

 * An author going by "persian85033" has produced an X Men Evolution fanfic involving, may God help us, the Single Minded Dectuplets Maria Xoaquina, Maria Xitlalli, Maria Xaviera, Maria Xacinta, Maria Ximena, Maria Xiomara, Maria Xochilt, Maria Xosefina, Maria Xulia, and Maria Xamila, who literally refuse to be separated even for the length of a single school period: the entire school has to be rearranged so that they can be in the same room for every class.
 * In Harry Potter and The Methods of Rationality it's stated that Fred and George have almost identical thoughts if they're given the same information. They only talk to each other to share something the other doesn't know about and on the very rare occasions that they disagree with each other they feel like something has gone deeply wrong. Apparently this is normal for magical identical twins and in times past families would actually kill one of the twins at birth.

Film
"Twin #1: We are getting aggravated.
 * The Corsican Brothers, as portrayed by Cheech and Chong.
 * In The Prestige,
 * The Twins from Matrix Reloaded, probably justified seeing as how they are computer programs.

Twin #2: Yes, we are."

"Fanty: Domestic troubles?
 * Don't forget Fanty and Mingo from Serenity.

Mingo: Domestic troubles?"


 * Although it's entirely possible they're doing this deliberately to mess with Mal.
 * Numbers 3 & 4 from the movie Nine, both of which are very skittish, are very curious about the world, and never talk.
 * Well, not quite. They do 'talk', so to speak...even if it is in their own eye-flashing language.
 * They also have projector eyes, or at least one of them does.
 * Skids and Mudflap from the Transformers film series, both portrayed as rednecks trying to be gangstas. Skids, however, is somewhat more aggressive and intelligent then his brother (and also has a slight case of hero-worship for Optimus Prime), even though Mudflap is probably the better fighter and driver.
 * The siamese twins from The City of Lost Children together called the "octopus".
 * In Dude Where's My Car, the twins that the heroes are dating spend all their screen time talking quickly and alternating with each other, and occasionally say the same thing in unison.

Literature

 * Fred and George Weasley from Harry Potter, at least superficially. See here for an analysis of their differences.
 * Rowling specifically envisioned slightly different personalities to the twins. Fred is braver and more outgoing and is the "leader," while George is more clever but meeker. For example, Fred is the one who initiates just about every hi-jinks they ever pull, and the one Ron complains about the most. The difference is very subtle due to their limited screen time, and their enjoyment of using this trope on their mother. To her credit, many found it surprising that


 * Sam and Eric from The Lord of the Flies. Throughout the book, their names evolve from "Sam and Eric" to "Sam 'n' Eric" and, finally, "Samneric", cementing them as one person. The only time they talk independently is after their camp is raided showing how effed up everything is getting. Even their description supports this idea - their skin looks stretched tight across their bones, as if they don't have enough skin between them.
 * The Duumvirate actively tries to fulfill this trope. Telling them apart is considered a major challenge even for their close friends.
 * In the Spider Robinson book Lady Slings the Booze, Arethusa is literally a pair of single minded twins, two women who from birth were telepathic with each other to a constant degree, combined with some weird superstition in their parents, caused them to grow up as a single person in two bodies.
 * The Twins from Eragon. They don't even have names. Ajihad says to Eragon "I would tell you their names, but they have none." They act pretty much the same, looking alike, acting alike, and having the same loyalties.
 * In another rare use of the 'One person, Two bodies' ploy, Miss Level, a village witch first met in Terry Pratchett's A Hat Full of Sky (Discworld), was born with two bodies, and people assumed her to be a set of twins, "then they thought [she] was evil." She lives a very prosaic existence for someone with two bodies. She meets an unusual end:
 * Ursula K. Le Guin's short story Nine Lives featured 10 clones who were essentially one being.
 * Ian McDonald's Desolation Road (set in the far future) had an incident with two clone-assassins, AlphaJohn and BetaJohn. They were two clones who were one being, with perfect telepathic connection, having the advantages of sharing all their senses. The victim realizes that . So he does that.
 * Rosencrantz and Guildenstern of Shakespeare's Hamlet are an example of characters who are not related, but function as a single character to the point that, according to some interpreters, other characters sometimes don't know which is which.
 * In Tom Stoppard's play, Rosencrantz and Guildenstern Are Dead, even they aren't always sure about their own names.
 * In The Abhorsen Trilogy by Garth Nix, there are the twins of the Clayr, Sanar and Ryelle. They speak in synchronization and it is noted that their souls are bound around eachother too tightly for even magic to treat them as separate beings. Though they do have some different traits - Ryelle is a better paperwing flier.
 * Used on two separate occasions by David Eddings:
 * In The Belgariad, Beltira and Beltika are like this before they become immortal sorcerors, and have both telepathy and millenia to become even more familiar with each others' habits and thought patterns. It's even effectively weaponised at one point, when Belgarath realises that their ability means they can cross-corrolate two sets of prophecies (one detailed but utterly random, one sparse but in chronological order) to find the similarities and make a comprehensive whole.
 * In Regina's Song the title character and her sister Regata are this, until the latter is raped and murdered, where they effectively become single-minded twins in a single body. Kind of. It's complicated.
 * Used in some form in A Breath Of Snow And Ashes in the Outlander series, with Jo and Kezzie. Yeah. It's a bit weird.
 * In Whispers, by Dean Koontz, the heroine was almost raped and killed by a famous man before killing him herself. He couldn't have done it because he was away. As you can guess, it was his twin. The other comes back and talks about how she killed him. Turns out
 * Mark Frost's The List Of 7 has Larry and Barry, identical twins and professional thieves. No one knew that they were indeed twins, so they posed as the same person. One of the brothers would appear in a pub or restaurant making a big show(one of the brothers liked to sing while the other liked to recite ribald limericks) while the other brother went to work cleaning out someone's flat. If one of the brothers was suspected, he could produce any number of witnesses to give him an alibi. When one of the brothers received a scar from a bullet wound, both brothers grew beards to cover the scar and maintain the fiction that they were the same person. Ultimately they were found out by Agent to the Crown Jack Sparks who pressed them into his service in exchange for a pardon for their crimes.
 * Ani and Tish act like this, but in reality Tish is almost three years older, they have different mothers, and Ani is almost a full faerie where as Tish is practically mortal.
 * Ritva and Mary Havel of the Emberverse begin very much like this, but in the course of the second trilogy they show/develop somewhat more distinct personalities.
 * Estha and Rahel from The God of Small Things, and this is Played for Drama, as they are frequently described as one soul split in two, and even describe themselves as "we" in the singular.
 * From Robert A. Heinlein's Time Enough for Love, Lapis Lazuli Long and Lorelei Lee Long, Laz and Lor for short. Their case is made even more interesting by the fact they aren't "natural" twins, but rather twin Opposite Sex Clones of protagonist Lazarus Long. The story plays their single-mindedness for humor, but they themselves are quite serious about it, claiming to possess Twin Telepathy and apparently practicing speaking in sync with one aother, because they enjoy messing with people's minds.
 * In The Vampire Files series, the Ruzzo brothers look and act so much alike, and work together so closely, that their fellow gangsters refer to them in the singular as well as the plural (e.g. "Tell Ruzzo to get their butt(s) in the car, already.").
 * Eustace and Claude from the Jeeves and Wooster series. At one point, when they're supposed to be heading to South Africa, they both independently fall for the same girl and independently leave the liner before it departs. They're then shocked to find each other when they both go back to Bertie's flat.

Live Action TV

 * Subverted on Odyssey Five, Kelsey and Bodanis, two of Neal's computer Geek friends are twins who are very similiar, but when the Very Special Episode about evil AI mindcontrol drugs came around, Kelsey was hit and Bodanis asked Neal for help.
 * In Quark, there are the Bettys (played by a pair of Doublemint gum twins) who can't decide which one is the clone (answer: the pretty one).
 * Corey and Trevor in Trailer Park Boys are a non-related example.
 * Mahou Sentai Magiranger's Nightmare Sisters aren't even identical, but almost all of Mea's lines amount to the last one or two words of whatever Nai just said. (Of course, they're both halves of a vampire queen who split herself because she got lonely.)
 * Must... not... make... joke...
 * Power Rangers RPM has Gem and Gemma, who don't appear to be capable of independent thought (or speech; the page quote is probably the only time they don't finish each other's sentences). For all intents and purposes, they are one person in two bodies. No explanation is made of this. In fact, its not even commented upon.
 * At least, not initially. Six episodes after their first appearance, they finally begin to be split up (though usually not by their own choice) and are given individual plot threads and slow-going characterization. However, it's doubtful they'll ever lose the singleminded-ness, except on the rare occasions they disagree on something (when they do disagree, its generally about romance, with Gem being overprotective of Gemma).
 * Double Trouble, a duo of recurrent villains in Where in The World Is Carmen San Diego. Their description reads: "Two guys, one mind, no shame".
 * Averted in Star Trek Voyager. When the oft-mentioned but never-seen Delaney twins from Steller Cartography finally make an appearance, one of them is attracted to Harry Kim, much to his annoyance as Harry prefers her sister. When a nonplussed Tom Paris points out that it shouldn't make any difference, Harry proceeds to list a number of character differences between the two, ending with "that cute dimple on her right cheek."
 * Battlestar Galactica Reimagined: The horde of Number Eights that confront Boomer in "Kobol's Last Gleaming" finish each other's sentences to creepy effect. Averted with Boomer herself, and Athena and a handful of other Eights that stand out. Averted by the Sixes constantly but played straight by the other models constantly.
 * It's eventually revealed that disagreements are settled by each of the twelve models voting as one, and Boomer causes quite a stir when she votes against all the other Eights.
 * Seventh Heaven with Sam and David. One wonders if the show runner has ever met real life twins.

Philosophy

 * In his book I Am a Strange Loop, philosopher-scientist Douglas Hofstadter describes an Alternate Universe called "Twinwirld", in which (almost) everyone is a pair of Single Minded Twins, called a "pairson". (Single births are called "halflings" and considered unbelievably pitiful.) This is an analogy for the two hemispheres of the brain.

Tabletop Games

 * Alpharius and Omegon from Warhammer 40 K are described as "two bodies with a single soul".
 * And their entire legion looks identical to him/them, so no one can single out their Primarch for assassination.
 * Dungeons and Dragons featured a race called the Dvati who were based on this trope. Each "individual" Dvati was a pair of empathically linked identical twins. They literally only have one soul(and by extension one set of hitpoints, divided evenly) between two bodies.

Theatre

 * Subverted in the stageplay version of Peter Pan. Two of the Lost Boys are twins, but Peter had never seen twins before they showed up and wasn't sure what to do with them. By the time the book begins they are simply each called "Twin" and are treated as one person. One is never without the other and they finish each others' sentences. Lampshaded when only one has a dream and the other says not to tell Peter because they 'didn't think they ought to have different dreams'.

Video Games

 * Timmy and Tommy Nook from Animal Crossing, who both say the same lines, with little gray words at the end representing the other one saying it at the same time.
 * Ami and Mami from The Idolmaster.
 * Now subverted with Idolm@ster 2 and by extension the new anime since Mami has grown her hair out and they no longer try to pretend to be the same person on stage.
 * Zorn and Thorn, from Final Fantasy IX. They habitually repeat what the other says, and merge into one freaky boss for their final boss fight.
 * In the backstory for Xenogears (as revealed in the games Perfect Works book)
 * An odd variation is taken in Rune Factory 2. Sera and Serina are twins who you are told are very different because one is "bookish", while the other is "sporty". In actual fact, however, they are separated in only one quest, where one begs you to reunite her with the other, at that, and not only like doing the same things, but count as one person in your menu, and giving items to one counts as giving it to the other. As a second-generation romantic option, dating one means dating the other, and they even complete (or simply repeat and enunciate upon) each other's sentences. Thanks to a probably-unintentional bug, they're even available as romantic interests to a female PC.
 * Ashley and Sidney Webber of Backyard Sports are like this. Achmed and Amir Khan have similar personalities, but have opposite abilities.
 * Koume and Kotome from Ocarina of Time. Despite representing two opposing forces of nature, they literally combine to create the most disturbing porn star ever.
 * In the Loose Canon comic of Team Fortress 2, Redmond and Blutarch Mann are this, much to their disgust.

Web Comics

 * In Schlock Mercenary, T'Chukk is from a race of bicameral lifeforms; he's a single being in two bodies, synced by radio. A bit of hyperspace communications augmentation, and he's able to be his own wingman in the crew's fighter craft wing.
 * Gemini Gold/Silver in Triquetra Cats
 * In Linburger, Firne are a single person in two identical twin bodies that change their sex organs with the phases of the moon (but always have boobs).

Web Original

 * Hamburger Pattie of the League of Intergalactic Cosmic Champions could split into two and become a Double Pattie.
 * Void Dogs has Nick Bradley, clone lifer (a subculture that emulates this trope through a mix of cloning and memory merging).
 * The popular YouTube video "Shoes" references this when the mother of a pair of twins asks "Don't they have the same thoughts?" Nothing could be further from the truth.
 * Parodied in Girlchan in Paradise, when two twin girls finish each other's sentences, are called "annoying" for it, then finally, are shot dead.

Western Animation

 * The Interesting Twins From Beneath The Mountain in Codename Kids Next Door.
 * Which is subverted whenever their plans (frequently) backfire on them. The female twin is shown to be easily angered and volatile while the male twin is calmer, submissive, and more sensible, but becomes dominant and protective when his sister breaks down when pushed far enough.
 * Sherri and Terri in The Simpsons.
 * Marge's sisters, Patty and Selma, started out this way, but diverged from each other over the seasons. Selma craves companionship, having gotten married several times and eventually adopting a Chinese girl, while Patty was earlier described as not liking to be touched, and more recently came out as a lesbian.
 * Jim and Tim from Kim Possible.
 * Also Wego; they even shared the same name. They have self-duplication as a superpower.
 * The Bully Brothers from The Perils of Penelope Pitstop.
 * Tomax and Xamot from G.I. Joe.
 * Walt Disney's Huey, Dewey and Louie, who were scripted, and treated, as one character in their earlier appearances. In the Disney Ducks Comic Universe, they're also often Finishing Each Others Sentences.
 * Charles and Mambo from Duckman.
 * Más y Menos from Teen Titans; they actually have to be touching to use their super-powers.
 * Hip and Hop from the Western Super Mario Bros cartoons, based loosely on the Iggy and Lemmy (who had no such relation) from the games Super Mario Brothers 3 and Super Mario World. Mario fandom is fond of the cartoon personalities of all the Koopalings, however, and so uses this trope but the games' names.
 * Notably averted in Invasion America, which had Sonya and Simon, a pair of psychically linked twins with super-powers which were stronger when they touched each other... and still gave them different personalities and independent character arcs.
 * Bill and Ben in Thomas the Tank Engine (and to a far lesser extent, Donald and Douglas, although they are more independent of each other).
 * Skarloey and Rheneas. Both started out as young and hot-tempered but at 140 years old they have mellowed out quite a bit.
 * Al and Moo Sleech from the Nicktoon Doug.
 * In the Batman Beyond movie, Dee-Dee/The Deeds/Delia & Deidre Dennis are twin sisters who may as well be two halves of one person. Besides looking and talking exactly the same (both twins are rapidly and amusingly voiced by Melissa Joan Hart), they move and fight in incredibly effective teamwork. Just goes to show how devastating it would be if villains didn't attack the hero one at a time...
 * In Justice League Unlimited they return for an episode set in a time travel corrupted future where they're given the power to duplicate, making even more copies with the same single mind.
 * They have been known to address one another as 'Dee Dee'; as in "You think so, Dee Dee?" "Oh yeah, Dee Dee."
 * Walter and Perry of Home Movies aren't related, but they are never apart (and almost always holding hands). Their less-than-totally-innocent relationship makes them essentially one character.
 * Ian and Jeremy from Barbie and The Diamond Castle.
 * Jetfire and Jetstorm from Transformers Animated. It's made all the more literal after they are badly injured and implanted with Starscream's programming during an experiment in allowing Autobots to fly. Besides being able to turn into jets, they gain the ability to combine into a single form known as Safeguard.
 * Tad and Chad on The Fairly Odd Parents are a variation. They aren't related, but other than different skin colors they could be twins.
 * Katie and Sadie from Total Drama Island are another case of unrelated friends who act almost exactly alike and are horrified at the thought of being separated. Interestingly, Fanon often tries to interpret or develop them to be more separate, while the show passed up a perfectly opportunity to do so (between Katie and Sadie's eliminations}.
 * Twirly and Whirly from the Bitsy Bears pilot.