The Cadanceverse is an Alternate Universe of My Little Pony: Friendship Is Magic by prolific Lunaverse author GrassAndClouds2. In a sentence, it can be summed up as My Little Pony: The Song Fic Universe.In this universe's backstory, both Celestia and Luna went insane. As their madness grew, they started to clash over the sunrise and sunset, about the precise point where one's rule ended and the other's began. Eventually, Star Swirl The Bearded proposed that they compromise by creating a golem-alicorn to control those two areas: and thus Mi Amore Cadenza was "born". The creation of a third alicorn delayed the inevitable for a hundred and fifty years, but eventually tensions between the two sisters broke out into open war, and on such a scale that Cadance was forced to act. Wielding the Elements of Harmony against her elders, she sealed them away, and began to rule in their place.A thousand years later, all is well in Equestria.Being a great lover of music, Cadance is in the habit of mentoring young musicians. One such student is cellist prodigy Octavia Philharmonica. Dedicated and brilliant, she studies her art relentlessly, to the point where she doesn't socialize with others. This worries Cadance, who points out that, at the very least, a musician has to work with others to perform professionally. Octavia, defending her habits, insists that she can do just that, and asks Cadance to give her a chance to demonstrate it. Cadance reluctantly allows Octavia to represent her at the Vernal Equinox Celebration, in Ponyville.It doesn't take long for Octavia to determine what Ponyville is planning for the Equinox. To her dismay, it is (by her standard) utterly mediocre, and she takes it upon herself to improve it. Trying to shove the square peg of what Ponyville likes into the round hole of what Octavia thinks is good goes about as well as you may think, and she soon finds the town against her, much to her incredulity. When things reach the point where it can't possibly get any worse, they do, in the form of Celestia and Luna breaking free. They promptly resume their old war, and Cadance flies after them to do damage control. Octavia (a nervous breakdown later), learns that several local musicians plan on making a perilous journey into the Everfree Forest. It seems that one of them had once heard a legend of a castle there, where the Elements of Harmony can be found...The Cadanceverse is open for other authors to write in, and has a group that can be found here. Some authors notes on the characters and universe can be found here and here.
This Fan Fic series contains examples of the following tropes:
Action Mare: All the Musical 6 to some extent, with Medley being the best example.
A Glitch in the Matrix: A leshy traps the group in an illusion that they're still moving, when really they've been moving in a circle. However, Octavia notes that the background noise hasn't changed, which cues her to the fact that something's up.
Agree to Disagree: Rarity and Fluttershy ultimately come to this decision in regards to their differing views on charity work.
Diamond Tiara is worse. While Silver Spoon is smug, self-centered and condescending, she at least has enough of a sense of decorum to not go out of her way to make others miserable, the way Diamond does.
Beam Me Up, Scotty!: When outlining her plan to deal with the Ursa Minor, Vinyl uses the oft-misquoted line "music soothes the savage beast". Octavia is quick to point out it's actually "savage breast".invoked
Bunny-Ears Lawyer: Vinyl. Despite her oddities, everything she does is aimed towards helping her become a better musician.
Call Forward: The Race That Ate Friendships has an early scene of Octavia going through her morning routine, including meeting several ponies around town. Hoe Down, written after but taking place several months earlier, has a similar scene Lyra showing Octavia around town to get used to it. This is meant to contrast how awkward Octavia was with the town at first with how comfortable she becomes later on.
Can't Hold Her Liquor: Medley. Octavia also gets tizzy pretty easily, but she at least has little experience with alcohol.
The Clan: The Apple family, of course, but also Vinyl's family. About fifty of them show up at the hoe down, and she says that's not even all of them. And they all look alike.
And Pinkie Pie, of course. Much to the supreme annoyance of Octavia.
Cuteness Proximity: Fluttershy's reaction to seeing the purified Celestia and Luna (who are both turned back into fillies). Bluenote has to remind her to breathe.
Damned by Faint Praise: Twilight tells Vinyl (completely seriously) that she could be good enough at magic to be one of Twilight's students. Vinyl gets very upset by this - goofy personality aside, she's a very hard-working pony who spends almost all her time improving her music, perfecting her equipment, and advancing her magic, as well as being the Element of Magic, and does not enjoy being patronized.
Dismotivation: Bluenote is a mild case; she didn't have enough drive to hone her skills to professional level. She's accepted this, however, and is happy with her current position as a music teacher.
The Ditz: Fluttershy's assistant, and Vinyl's niece, Cat Scratch.
Do Not Call Me Paul: Apparently, "Vinyl" is just a nickname. Her actual name is Virola, and she does not seem to like it.
Dubstep: Vinyl calls it "Wubstep". Octavia calls it awful.
Rainbow Dash and Ditzy Doo have this in regards to their shared goal of getting into the Wonderbolts. Lyra, though, seems to think it's just a cover for some UST. Judging by the events of the hoe down, she's right.
Friend to All Living Things: Fluttershy from the Musical 6. Zecora is this as well, going to substantial lengths to protect a wounded, trapped kraken.
Full Name Ultimatum: Vinyl's mother calls her by her full name, Virola Yvonne Scratch, when mad at her.
Genki Girl: Vinyl, whenever on stage, and Lyra, whenever awake.
Golem: Cadance is one. The C6 also have to fight one as their final obstacle before they reach the Elements of Harmony.
Heroic BSOD: Octavia loses it after Shining Armor and Pageturner tell her what they think of her.
Heroic Self-Deprecation: Fluttershy views herself as a horrible pony for spending money that could otherwise go to charity on herself, even if only for a minor luxury like buying a nice dress.
Octavia berates herself whenever she feels that she's performed some shortcoming or failure as a friend.
Hypocritical Humor: Octavia's comments about the absurdity of Bon Bon's Super OCD system of storing things in her kitchen is immediately followed by an example of her own obsessive scheduling habits.
Identical Stranger: Fiddlesticks' resemblance to Octavia is touched upon, but not directly addressed. And Octavia herself is oblivious to it.
Innocently Insensitive: As stated above, Silver Spoon can sometimes be mean even when she thinks she's being nice.
Bluenote doesn't mean to insult Octavia's mother's naan recipe, but her improvisation towards baking it, and her laughing off the poor results, makes it seem like she's mocking Octavia's fond memories of baking it with her mother.
It's All About Me: Octavia, although not as bad as many others with this trope, has a certain loss of perspective. It doesn't occur to her that Medley would be anything less than thrilled to show off her wares to Cadence, and she concludes that the reason why Ponyville likes crap music is because they don't know what good music is. Once she realizes she has this flaw, she dedicates a lot of her time to trying to fix it, and worries that she's slipping back into bad habits.
Loose Canon: The story "Blitz Carmen" is listed as possibly being in-universe fan fiction.
Lotus-Eater Machine: Nightmare Moon's final trap to stop anypony from reaching the Elements is one of these. It almost works, too, trapping five of the Musical 6 in their own personal paradises (Octavia gets a life of solitude to perfect her craft; Medley owns a prosperous business; Lyra marries Bonbon; Bluenote indulges her hedonistic desires and loafs about; Vinyl is the most famous DJ in Equestria and performs at all kinds of epic concerts). Only Fluttershy can resist, because she is too focused on caring for others to allow herself to rest in her own paradise.
Mad Scientist: Carrot Top is a comedic one, always seeking new developments in farming and food, usually with hilarious results when things go wrong.
Missing Mom: Silver Spoon's mother's absence is apparently planned to be a plot point in her story arc, though GrassAndClouds2 and the other contributors are still debating in what way.
Mythology Gag: At the end of the hoe down, Applejack leads the town in a version of "Raise This Barn" dedicated to honoring the Elements of Harmony.
Nice to the Waiter: Implied to be the case with Silver Spoon's relationship with her maid Betty Buttle, if only because she's been with her family for years, whereas Diamond Tiara's servants usually quit after a few months.
Noodle Incident: Fluttershy once let Lyra crash at her place after Ditzy and Raindrops dropped a piano on her house.
Vinyl once got into a drinking contest with Big Macintosh that ended with them filling the town fountain with cider and jumping into it.
Trixie apparently once accidentally launched a firework into a Duke's mansion.
When asked why Red Tape dislikes her so much, Vinyl only says that it's a long story, and that "the fire wasn't that bad".
Bluenote and the foals she was escorting get lost during the Running of the Leaves, and when they finally show up at the finish line, Vinyl asks what took so long. Bluenote's response:
"The usual; got a bit off track, found a tribe of pygmy elks in the forest, saved them from a horde of ravenous miniature giant space hamsters. Me and the foals got crowned as princesses, even Titchy."
As a bonus, Lyra asks about the elks' queen, implying she's met them as well at some point.
Vinyl's wub cannon once malfunctioned and trapped Scootaloo in a tree since it kept firing at her when she tried to get down.
Apparently the last time Medley got drunk, she somehow ended up on top of Town Hall with both a mare and a stallion. It happens again after the hoe down.
Carrot Top apparently once brought some trees to life somehow.
No Social Skills: Octavia thinks that Trixie is some kind of expert in friendship because everypony likes her. It's clear to the audience, however, that they only like her because she parties like a rock star.
Royals Who Actually Do Something: Princess Cadance has been helping to run the nation for a millennium, of course, and she also teaches music to her students. Additionally, Prince Blueblood (of the friendly nation of Monacolt) is similarly active, and is also mentioned to be quite a skilled boxer and harpist.
Robo Teching: Knowledge of Syncopation (playing back-beats a little too early or late) allows Vinyl to change her spells paths.
"No colt's fair like Blueblood!" "Debonair like Blueblood!" "Nopony's cologne sweetens air like Blueblood's!" "His scent, I've been told, is intoxicating!" "My what a guy, Blueblood!" —Rarity and the ball crowd
Chess, with the Ponyville citizens singing 'Merano.' It's been noted that this is one of GrassAndClouds2's favorite musicals.
Upper-Class Twit: Trixie. She travels Equestria throwing huge parties and putting on magic shows, spending vast amounts of money to do so. As the heir to the Duchy of Neigh Orleans, she can afford it.
Villainous Breakdown: Both Burning Sun and Nightmare Moon fall apart in panic when the Musical 6 activate the Elements of Harmony.
Villains Never Lie: Octavia realizes that Burning Sun and Nightmare Moon are telling the truth about Cadance being a golem because they're both sticking to the story; if one was lying, the other would expose it to knock them down a peg.
We Used to Be Friends: After Pageturner chews out Octavia, she disowns her as a friend, and refuses Octavia's later attempt to make amends.