Ensemble Darkhorse/Western Animation/My Little Pony: Friendship Is Magic

A lot of background characters in My Little Pony: Friendship Is Magic have garnered a lot of praise and attention from the Periphery Demographic, despite several of them not having any lines and a few more only making a few background appearances. Because of this, for the sake of neat archiving, the Ensemble Darkpony characters can be listed here.

Supporting Cast

 * Even some of the Mane Six were taken from previous generations of My Little Pony cartoons and toys, where they played relatively minor roles. Applejack only appeared in the original 1982 pilot as one of Firefly's friends, Rarity was a one-off character in G3, and Fluttershy never even appeared in the cartoons - she was just a Palette Swap in the G3 toys. Bringing back Applejack with her G1 design is one of the reasons old-school My Little Pony fans rejoiced about this show in the first place.
 * Princess Luna (also a literal example of a Dark Horse who's part of an Ensemble) appeared for less than a minute in the second episode, said two lines, and wasn't even mentioned again until the first episode of season 2. Fans desperately wanted to see her return regardless, and there are tons of drawings, stories and discussions about her, flooding fan fiction websites, forums, and chat boards. When she was confirmed to return for season 2, And the Fandom Rejoiced was a gargantuan understatement.
 * Luna managed to do this again after her real appearance in "Luna Eclipsed", which was received exceptionally well among fans (in no small part due to her hilariously overplayed and lampshaded Flowery Elizabethan English and No Indoor Voice) and superseding nearly all other portrayals of her. Cries of "Redo ALL the fanon!" were heard for a while.
 * Nightmare Moon is either another element of Luna's popularity or an entirely different Darkpony herself, depending on whether she is considered a separate character or simply an extension of Luna (although considering the ending of "Luna Eclipsed", she is more likely the latter).
 * As one of the few recurring male characters, Big Macintosh has a bit of a fan-following. In Season 1 he mostly just had cameos when Applejack was involved, but in Season 2 he became more and more involved with the main & supporting cast. He also proved to be popular enough to receive a blind bag toy, making him one of the first stallions to receive any kind of toy since G1.
 * The Grrreat and Powerful Trrrixie has an very impressive fanbase for a one-episode character with little significance, and her prominence in fan works almost reaches main character levels. Much like some other darkponies listed here she received a few toys based on her, at first calling her Lulamoon, but then changed to "Trixie Lulamoon".
 * Of the main cast pets, the two most popular are Fluttershy's bunny Angel and Pinkie Pie's baby alligator Gummy.
 * Cheerilee was and still is a popular target for fanart and fanfiction from her very first appearance, being a teacher a good excuse to include her in any number of scenarios. Her popularity only grew during season 2, which gave her more screen time and even her own episode, "Hearts and Hooves Day", in which she featured alongside fellow darkpony Big Macintosh.
 * Discord is the single most popular antagonist, loved and loathed in equal measure, and continually pops up in drawings, stories and speculation even long after being sealed away again, an enormous section of the fanbase wanting him to make a reappearance. Not at all hurt by him being a blatant (admitted) Expy of Q, to the point where he's played by the same person.
 * Daring Do, the star of the Book Within a Show that Rainbow Dash becomes a fangirl of in "Read it and Weep", . She appears in "Read It and Weep" as the protagonist of the book Rainbow Dash was reading. Her being an Indiana Jones expy has made her really popular material for fanfics and art. Many pictures of involving Rainbow Dash have a tendency to include her in some form. (Such as a book or a plushie.) Heck, she acquired enough love to have a rather detailed Just For Fun page all to herself. (And it is massive.)
 * Queen Chrysalis came out of nowhere, only hinted at once (in an online New York Daily News article) during all the crazy hype The Hub and Hasbro did for the season 2 finale, most of which was focused on the other new characters Princess Cadance and Shining Armor (since they're the ones with toys), and took the fandom by storm. All the fanart created literally within a day of her appearance shows just how far being a competent and dangerous villain with a unique design and magnificent Villain Song will get you.
 * Soarin' and Spitfire of the Wonderbolts managed to capture a lot of attention amongst the fanbase when their names and personalities were established in the Season 1 finale . Spitfire especially became somewhat of a pinup-girl to the fanart community with many a saucy WW2-style cheesecake image being drawn of her, as well as plenty of fanfics. Spitfire was brought back for another speaking role in Season 2 where she was established as the captain of the Wonderbolts, and Soarin' got a cameo in the Royal Wedding where he was seen wearing a military dress uniform and dancing with Rainbow Dash.
 * The Flim Flam Brothers, having an extremely catchy Villain Song makes them stand out.
 * It should be noted that every time a new character, even a one shot for the episode, appears they spawn at least some fanart and an Ask a Pony page within 24 hours of a new episode airing. No exceptions.

Background Ponies

 * Nearly every single background character is given at least a name by the fans, if not an entire personality and history (especially if they have a unique design), and they'll receive fanart within a day of airing. Below are above & beyond the most popular and the ones the fandom is most familiar with.
 * Pointed out, and made fun of with this picture.
 * No discussion on Ensemble Darkhorses is complete without mentioning Derpy Hooves (sometimes referred to as Ditzy Doo), the Recurring Extra that's gotten the most love from fans and the show's staff. In a background shot of episode 1, a grey pegasus pony with "derp" eyes was spotted, and swiftly Derpy was born, a strange but surprisingly competent mailpony who loves muffins, often derps reality, and in spite of her difficulties is very friendly and hard-working. In "Feeling Pinkie Keen", she even managed to become a combination Ascended Meme/Ascended Extra, Lauren Faust herself said "She can be Derpy if everyone likes" (during production of season one, none of the background ponies had official names), and in season 2 she's gotten her own little gag scenes. Not bad considering her googly eyes were just a random joke thrown in by one of the animators.
 * Her astronomic popularity even extends to other background ponies. When a unicorn filly with similar coloring was spotted it led to the creation of Dinky Hooves, Derpy's daughter. One of the few things fans agree is that Derpy and Dinky are a happy family (sometimes married to Doctor Whooves, mentioned below), and Dinky is the most popular child character outside the Cutie Mark Crusaders with tons of fanart and fanfics involving the two, often resulting in hearts being melted.
 * Her Ascended Meme status is completed in "The Last Roundup", where the first scene after the credits features Rainbow Dash actually having a whole slapstick routine with her, where she gets several lines and is addressed as "Derpy".
 * When "The Last Roundup" suddenly disappeared from iTunes, then later restored with Derpy's scene modified with tweaked dialogue (she was no longer referred to by name and had a different voice), the fandom absolutely exploded with panic and anger towards Hasbro, displaying the sheer level of reverence that had been given to the pony. Ultimately, the explanation for the change was that there were complaints Derpy was a stereotype of the mentally disabled, and the arguments about this among the fans were often heated and ugly.
 * Even the official merch is not safe from the power of Derpy. She now has her own figurine, the 2012 limited-edition pony for San Diego Comic-Con and the Orlando MLP Fair. Complete with derped eyes and muffin box art!
 * Season 5 has given Derpy back her voice! And this time its almost exactly the same voice used in the fan portrayal "Doctor Whooves and Assistant", which was essentially the iconic Derpy voice among the fandom! And she had a partner act with Dr. Whooves in the episode "Slice of Life"! WHOO-HOO!
 * 'Slice of Life' also officially changed her name to 'Muffin' (its in the credits), but exactly zero percent of the fanbase is paying any attention to that. Its noteworthy in that on-screen, nopony ever addresses her by name; they might have been obligated to change her name in the credits due to complaints, but they know exactly what the fanbase will do if they ever make the change actually explicit in-setting.
 * Lyra Heartstrings, a mint colored unicorn with a lyre cutie mark who is often seen hopping up and down with an excited look on her face as if she's mugging for the camera or engaged in a Funny Background Event, most notably sitting or otherwise acting in a semi-human like manner. It became one of the fans (many) memes to depict Lyra as the pony equivalent of an Otherkin, wanting in one way or another to be human (despite there being no sign humans even exist in Equestria). She was nicknamed just "Lyra" by the fandom, and this name was adopted by WeLoveFine, then she was officially named "Heartstrings" by Hasbro. This caused a bit of confusion, but some fans opted to Take a Third Option and call her "Lyra Heartstrings", and apparently Hasbro thought this was a good idea as well, with her full Ascended Fanon name in the Pony Wedding brushables and the fifth wave of the Blind Bag toyline. Finally, after two seasons of complete silence, she finally got to speak a few lines in "A Canterlot Wedding".
 * Lyra often appears alongside a pony that appears to be an Expy of Bon Bon from My Little Pony Tales, originally due to the way their colorations complimented each other (as is standard practice with the placement of background ponies in crowd shots). This circumstance resulted in a lot of fan works depicting the two together in some way, whether as best friends, roommates, or romantic partners, and while Bon Bon doesn't get nearly the same amount of attention on her own as Lyra does the two together are the most widely accepted pairing, and basically the One True Pairing of the fandom. This is yet another aspect of fanon that has been recognized in official media, such as being intentionally placed together in the famous Comic Con poster and participating in Funny Background Events in several episodes (such as "Secrets of My Excess", where they share one with Derpy).
 * As of season 5's "Slice of Life" (get used to seeing that reference here, it was an episode devoted solely to providing focus on background ponies), Lyra and Sweetie Drops/Bon Bon are canon "best friends", with heavy heavy overtones of ship tease.
 * A male earth pony with a spikey hairstyle that reminded some fans of David Tennant and an hourglass cutie mark was christened Doctor Whooves by fans (or "Doctor Whoof" if you prefer, but the show runners seem to like "Whooves" better), spawning endless crossovers and the fanon that Equestria has (or had) their own version of Time Lords. Word of God says his look is, or initially was, a coincidence; his fandom interpretation was alluded to by his manning the hourglass in "The Super Speedy Cider Squeezy 6000", lording over time in a way.
 * Other ponies bearing hourglass cutie marks have also been declared Time Lords. So far three other background ponies with an hourglass cutiemark have been associated with Doctor Who, mostly because they look far too much like Matt Smith (in a tuxedo and top hat), Peter Davison, and Jon Pertwee to be a coincidence.
 * A female DJ unicorn that appeared for less than five seconds in "Suited For Success", doing nothing but turning on music and bobbing her head, garnered a huge following, generally called Vinyl Scratch, though other fans insist on her stage name, "DJ P0N-3". The "DJ Pon-3" name was actually acknowledged in The Hub's Equestria Girls and There's a Pony For That commercials, and she's one of the few extras to receive her own official t-shirts and a brushable toy. She eventually returned in "A Canterlot Wedding - Part 2", this time showing what color her eyes are underneath her Cool Shades (the most popular fan theory was that her eyes were red -- they turned out to be magenta).
 * And her human counterpart actually got to help save the main cast during the climactic battle of 'Equestria Girls 2: Rainbow Rocks'.
 * Octavia, one of the musicians who first appeared in "The Best Night Ever" (the cello player), obtained an enormous amount of attention from fans, with stories and drawings galore, and even her own theme music!. Her resemblance to one of Pinkie's sisters also fueled a lot of Wild Mass Guessing for a while. Pretty amazing considering she had pretty equal screentime with her bandmates in her first appearance. She's since appeared on the Comic-Con 2011 poster/desktop background, gained a Palette Swap in "Luna Eclipsed", returned to the show during "Sweet and Elite", been included in the Valentine version of Card Creator, and been featured on the licensed shirts and art print Musical Pony Battle, Octavia Disdainful Glance, and Dancing Ponies.
 * 'Slice of Life' also canonizes the popular fanon of Octavia and Vinyl Scratch being roommates, and also has them performing an epic dubstep/cello duet. Noteworthy in that despite them being an Odd Couple as popular fanon, this was the first time they had both appeared in the same episode at all.
 * Golden Harvest, a yellow earth pony with an (usually) orange mane, gained some popularity due to a popular fan comic depicting her as Derpy's roommate or best friend. Fanon usually has her as the Straight Mare to Derpy's goofiness (which got a Fandom Nod in "Luna Eclipsed") and there's a Running Gag about Derpy constantly emptying her fridge. Notably, she is one of the background ponies that's spoken the most in the series and has a memorable gag scene in "Boast Busters" where her hair is briefly green, so that probably helps her popularity a bit. She's was originally (and occasionally still is) known by the Fan Nickname Carrot Top, since she didn't receive her official name until the third wave of the Blind Bag toyline.
 * Berry Punch (aka the Over Protective Parent Pony), a pink/purple earth pony with grapes for a cutie mark, is known for hastily dragging what might be her child inside in "Bridle Gossip" and drinking directly out of a punch bowl in "Call of the Cutie". The latter has led to her being depicted as The Alcoholic in fanon, an idea apparently shared by the storyboard artists when they put her into the scene, as revealed during an interview. She often gets paired with Minuette/Colgate due the two singing together on a hill during the "Winter Wrap Up" song.
 * A common participant in the "Brushie Brushie" meme is Minuette, a background unicorn that's a blue Palette Swap of Sea Swirl and has Doctor Whooves's hourglass cutie mark (fun fact: she appeared in the series before either of those two). Most fans call her Colgate for her toothpaste-striped hair and the associated meme, and even has her own fan-made theme. Alternatively, she's known as "Romana T. Colgate" (after the female Time Lord who accompanied the Doctor for a while), because apparently having an hourglass cutie mark means you're a Time Pony. She may have even gotten her own Fandom Nod in "Luna Eclipsed", when her costume for Nightmare Night may have been a dental surgeon.