Non-Identical Twins

"It really looked like her... just like Noel!"

—Rina of Mermaid Melody Pichi Pichi Pitch, who apparently can't tell a Broken Bird with curly purple hair from a Yamato Nadeshiko with wavy dark blue hair.

Robotnik: Voila! Your identical twin brother!

Scratch: My twin?! Am I that ugly?

—Adventures of Sonic the Hedgehog

A Characters and Casting trope, the polar opposite of Making Use of the Twin: so you have this classic play you want to put on, a comedy about two identical twins that people keep mixing up... but wait - your theater company doesn't have two identical twins! What to do?

Some directors would try to cast two actors who look similar enough that in identical costumes and make-up they might almost pass as twins, but if your play is a comedy it can be even more effective if you cast two actors who look nothing whatsoever alike - and simply handwave the fact that none of the other characters can tell them apart. If you take this second option, what you have is Non-Identical Twins.

This is generally a comedy trope, and often a theatre trope because, for whatever reason, people have a harder time suspending their disbelief for something like this if it happens in film—presumably because we expect a movie to be able to fake a truly identical-looking twin in ways a play could not.

It works comedically because the "mixed-up identical twins" plot is fairly ridiculous to begin with, and this hangs a giant lampshade on it.

Not to be confused with fraternal twins (actual non-identical twins) or Half-Identical Twins. This only counts when the twins are obviously meant to be identical, but their identical-ness is an Informed Ability. Exists because of Always Identical Twins.

Examples of Non-Identical Twins include:

Anime and Manga

Ranma ½ did several of these, often playing on the Magoo-like eyesight of Mousse. One memorable one not involving Mousse had Ranma disguise Katsunnishiki (a sumo pig the size of a rhinoceros) as Ranma's fiancee Akane, complete with wig and a schoolgirl outfit. Akane was not amused.
In Urusei Yatsura, a fox spirit showed up at the school and tried to pull of several impersonations. But it was always one foot tall and an obvious anthropomorphic fox. However, when it impersonated the teacher Onsen-mark, the students (who didn't like Onsen-mark) proclaimed him the real teacher, tied up Onsen-Mark, and beat him for "impersonating the teacher", all the while referring to Onsen-Mark as "The Hoax".
Terriermon and Lopmon aren't twins, but still got the accidental switch done in the second Digimon Tamers movie when Henry took Lopmon (who is chocolate brown and pink with two more horns).
As evidenced by the page quote, Caren and Noel of Mermaid Melody Pichi Pichi Pitch. Kaito and Gackto, too.
Kanchomé's debut episode in Zatch Bell has him and Folgore boarding Kiyomaro up against the ceiling. Then Kanchomé transforms into Kiyomaro and tries to get Gash to reveal the location of the book. It's almost a perfect match... except his nose is huge. Even worse... neither Gash nor Kiyomaro's school friend Suzume can tell the difference - although to be fair, Suzume is a huge ditz and Kanchomé compliments her beauty before she has a chance to notice. Gash has no excuse, though.
- This is funnier in the anime as Kanchome's VA sounds nothing like Kiyomaro's and in fact sounds exactly like Keiichi Morisato (who's voiced by the same person), a kindly person whose character is not at all like Kiyomaro.
Agon and Unsui of Shinryuji from Eyeshield 21, with Agon having long, black dreads and glasses and Unsui being completely bald. When Agon shaves his head, however, it turns out they're exactly alike.
- Yeah, but the only people who mixed them up were the ones mailing out awards since they had the same last name and applied for the same scholarship, which had nothing to do with their physical appearance. They're only hard to tell apart once Agon shaves his head.

Comic Books

German artist Walter Moers once wrote a short comic about "the cruel twins". At first the two mean-looking guys yell about how evil and cruel they are, but when they go into details, we see that they're actually extremely nice and gentle in their deeds. At the end, they admit, yes, they aren't cruel at all, and no twins either--"we just look similar". Which, you guessed it, also isn't the case.

Film

There was some movie that featured a wealthy man using his poor, long-lost, nearly identical half-brother to fake his death. The half-brother survives but with Laser-Guided Amnesia, and his doctors and his cute nurse try to get him to remember his life - or rather his brother's life. The twist is that the rich brother is played by a white actor while the poor brother is played by a black actor. Naturally, the whole film is a meditation on identity. The poor brother eventually gets to have his cake (his memory) and eat it too (when the rich brother tries to kill him and gets killed instead. The poor-now-rich man lives happily ever after with the cute nurse.
The Great Muppet Caper had a running gag where Fozzie and Kermit were supposed to be twins that could only be told apart because Fozzie wears a hat.
- No, it's that they can only be recognized as twins when he removes the hat. It's that kind of Movie.
Stuck On You had Greg Kinnear and Matt Damon as conjoined twins who share at most hair colour. What's interesting is they manage to convince some people they aren't conjoined but these people don't then just point them out as twins, suggesting they aren't meant to be identical, but I recall no explanation for how you get frateral conjoined twins.
- This troper seems to remember something about Greg Kinnear having been damaged in the womb or something, and that's why he looks so much older than Matt Damon - presumably when Damon is that age, he'll look like Kinnear?
  - Damon's character got most of the liver, which they shared, so Kinnear didn't age as gracefully.
In The Krays, the roles of identical twins Ronnie and Reggie Kray are played by real-life brothers Gary and Martin Kemp. But while they do look somewhat alike, they are not twins. The use of real twins to play the characters as children doesn't help. That said, the Kemps do turn in compelling performances.
The 2011 Tintin film has Comedy Duo and Those Two Guys Simon Pegg and Nick Frost (who look entirely different) playing the Thompson twins. Then again, while they look alike in the comics they each spell what is presumably their surname differently.. so god knows what's going on.
- Actually Thompson and Thomson (or Dupond and Dupont as they're originally named) aren't twins. They're just Heterosexual Life Partners who happen to look very much alike.
The Disney Channel movie Double Teamed, based on the true story of twin basketball players Heather and Heidi Burge had a very mild version of this. While the twins weren't identical, they did look very much alike. The actors who played them looked alike, but weren't the same height. One actress had to wear lifts in her shows.
The "high concept" of Twins. Of course Danny DeVito and Arnold Schwarzenegger look alike!

Live Action TV

Jade and Kirsty Sutherland from Home and Away. This was explained eventually that Jade accidentally got swapped with another baby when the hospital goofed.
On Friends, Joey tries to pull this on some researchers conducting a twin study. No-one is the slightest bit convinced.
The Suite Life of Zack and Cody has an episode where Maddie and London make plans to date twins. Unfortunately, Maddie realizes that the twins are fraternal when they see that the second brother is short, skinny and nothing like his handsome and charming brother. She has to date him.
- There was one episode where the title characters themselves were treated as identical. It was they typical situation where one has made two dates, but neither was a blind date.
A plot point in an episode of Law & Order, as the witness can tell the gangster apart from his twin brother he is trying to claim did it because, despite being identical twins, they have lived much different life-styles, resulting in many physical differences, which are very noticeable because the witness was a nurse.
An episode of News Radio had this as part of the plot. Matthew's 'twin brother', played by pre-Daily Show Jon Stewart, came to visit. He looked nothing like him, but they both kept playing 'look alike' games. Eventually Matthew's brother says that it was a stupid idea of his parents in order to misdirect Matthew from thinking he was adopted. The rest of the cast is shocked, as this is incredibly stupid, even for Matthew. It turns out that the deception was the other way around. Matthew was the biological son, and he was simply playing stupid in order for his brother to not think he was adopted.
In Sykes Eric and Hattie insisted they were identical, despite not only being the opposite sex but also being completely different body types (Eric being taller, thin, and rakish and Hattie being shorter, heavier set and baby faced).

Music

In a rare non-television or film example, there is a Hong Kong pop duo called The Twins, made of Charlene Choi and Gillian Chung. The two are not related and look nothing alike, give or take a few people who might think they do.

Professional Wrestling

There's a Professional Wrestling duo described on this wiki somewhere where one of the "twins" is white and the other's black.
- Most likely referring to the Dudley Boys/Team 3-D--who in fairness, are not actually twins, but "Brothers From Another Mother".
- It might have been. I do recall something like that, and a joke that they would constantly pull the old "identical twin swaps places with his brother during a tag team match while the referee is distracted" trick. Which worked!

Theater

A wonderful production of Shakespeare's The Comedy of Errors had the leading pair of twins played by a tall, thin black guy with very short hair, and a short, stocky white guy with a ponytail. Their only physical similarity was their identical Blues Brothers-inspired suits. Naturally, they were indistinguishable to everyone but the audience.

Video Games

Travis Touchdown and Henry in No More Heroes.
Kyosuke and Hyo from Rival Schools.
Solid and Liquid Snake in Metal Gear Solid are identical twins. However, due to genetic altering on Liquid his recessive genes became dominant (roll with it), causing him to look nothing like his brother despite having the same DNA. Somehow.
- It's heavily implied that their faces are identical. Meryl states several times that Snake looks just like Liquid.
- One of the VR missions deals with having to determine which soldier is lacking their glasses. You do this by equipping a blonde wig and walking in front of a row of guards. The guard who raises his rifle is the one with the bad eyesight.

Web Original

In the sci-fi web series The Crew, no one can tell the black guy apart from his clone, who looks nothing like him aside from being black, and their not even the same shade. (The other clones, on the other hand, are completely identical aside from the fake mustaches they're inexplicably wearing).

Western Animation

Scratch and Grounder of Adventures of Sonic the Hedgehog are revealed to be twins in the first episode. Scratch was not amused when his twin rolled off the assembly line. Then again, it was Scratch's fault that Grounder didn't become an exact copy of him like Robotnik had planned. And soon a Sibling Rivalry begun, as both of them claimed to be the favorite (Scratch because he had been built first and Grounder for having more accessories). This trope was actually referred to by name in the first comic they appeared in.