This story is a sequel to How Not To Use Your Royal Prerogative

  In an Equestria where the Sonic Rainboom never happened, Sunset Shimmer is the prized pupil of the Princess of the Sun. As Sunset struggles to make up for her past misdeeds and come to terms with the pony she wants to be, Celestia sends her to find the classic work The Application of Unified Harmony Magic from the Royal Canterlot Archives.
  Right after lunch, some meddling by her friends and meeting somepony with firsthoof experience of the Sunset she used to be.

Featured on Equestria Daily on August 18, 2016!
Appeared in the FimFiction Featured Box!

Cast: Sunset Shimmer, Moon Dancer, Minuette, Twilight Sparkle & Princess Celestia

Stories set in the Wavelengths Timeline in chronological order:

Origins Arc
The Alchemy of Chemistry
Bards of the Badlands
Grading on a Bell Curve
Habits of the Equestrian Phoenix
How Not To Use Your Royal Prerogative

Applications Arc
The Application of Unified Harmony Magics
Princess Celestia: A Brief History
The Cloudsdale Report

Dreamers Arc
Tactics of Snowbound Unicorns
A Study in Chaos Theory
Teahouses of Saddle Arabia
As the Raven Flies

Cover Credits
Cover Design by Amber Spark
Sunset Shimmer Vector by TigerBeetle
Pony SciTwi Vector by Osipush
Canterlot Bookshelves Vector by FavoriteArtMan
Sunset Shimmer Cutie Mark by MillennialDan

Beta Reader Credits
Ebon Quill - Worldbuilding Writer on The Manehattan Project
Quantum State - Technical Director of The Manehattan Project
The Albinocorn - Master of Sunset Shimmer Stories

Strongly Recommended Stories:
The Brightest and the Best by Pineta - The events in this story are considered to be completely canon to this timeline and explain Twilight's entrance exam to Celestia's School for Gifted Unicorns. I cannot recommend this story enough.
MLP Annual 2013 - "The Fall of Sunset Shimmer" - As above, the 8-page short comic in the beginning of the Annual is also considered to be canon, though with some major variations.

Version 3.0 Edit: Extensive grammatical and mechanics changes. Adjustment to timeline of Sunset's second mirror experience.

Every pony in Equestria knows the names Octavia Philharmonica and Vinyl Scratch. Every musician in Equestria knows and reveres their talent and most semi-jokingly complain that Octavia and Vinyl's relationship should count as a monopoly on musical talent. Very few know their early story, years ago when Octavia had only just left Canterlot Conservatory and Vinyl was... well, being Vinyl.

This story is a sequel to Fashion Crush

(Humanized) Vincenza Scratch, AkA Vinyl for her friends, AKA DJ-PON3 on stage, 22 years old. The DJ found herself in one of the low periods of her young career, probably the lowest and longest she ever experienced so far; writer's block, out of ideas for a new genre of music as her 'classic' electronica seems to go out of the crowd fashion, less and less attendance to her gigs, etc.

Starting to run low on money, She gets in touch with one of her mother's friend in the capital, Vito Philharmonica; Member of the board of one of the most prestigious private high school. Vito offers her a place to stay and a job to help her to get back on track : A music teacher job for a Highschool senior class, which includes Vito's own daughter, Octavia.

How's Vinyl going to teach to a bunch of teenagers when she's barely older than them? ( and probably not much more mature as well). And when other teachers and some of her students look down at her for being a 'simple' DJ? One answer, Becoming the GTVS: THE GREAT TEACHER VINYL SCRATCH! (Yes inspired by GTO, one of the coolest manga ever)

Fanart for the story on tumblr or on DA!

Don't forget to check the comic version as well

Sunset Shimmer has just graduated from Canterlot High School, and while that would normally be cause for celebration, it fills her only with a nameless dread as her friends begin to scatter to the winds to pursue their futures. With the latent magic of the human world contained and categorized and the Rainboom's idyllic days of schoolwork over, she finds herself without aim and listless, as though something important is missing from her life.

Fortunately for her, Princess Twilight Sparkle might know what ails her.
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So. First time posting on the site after a VERY long period of lurking and reading and enjoying the tales this fandom can produce. To my surprise, I found a dearth of a certain subset of story that I wanted to read, and so I have done this, to put my thoughts to words. After all, it is said that one should write the story they want to read, yes? I've been inspired by a variety of stories like it that came before, and I hope to equal their quality.

I'll try to update roughly once every couple of weeks; please be patient with me and I hope you give this tale a once-over. Pre-emptively tagging with AU, that I might diverge freely from what may come if needed.

Princess Celestia has trained her three apprentices, Sunset, Trixie and Twilight, to become the newest generation of the Knights of the Realm, protectors of Equestria. Their abilities and morals are unquestionable, and they're also perfectly willing to become the heroes Equestria needs. However, something had to give, and in the process of turning them into the future Legendary Heroes, those three ended up becoming particularly eccentric in their methods and quirks. This is the start of a very silly era of heroes.

October 2019 Edit: The story's rating has been changed from E to T.

This story is a sequel to Ponyville Sunlight

After agreeing to be her date, Princess Twilight Sparkle crosses the portal to accompany Sunset Shimmer to the prom. They're not going alone of course; Sunset's human friends are coming, too. With good friends, beautiful dresses, fancy dinners, and formal dancing, Twilight thinks she's really going to enjoy the prom. Of course, what Twilight and Sunset are looking forward to most is spending more time with each other. The prom will certainly be a night to remember.

NOTE: Rated T for implications. Nothing explicit, here. It's my usual self with going just a bit farther but nothing explicit.

Third story in the Rays of SunLight series.

She's an ally of justice!
With powers of the sun, she smites villains that plague this world and rescue those who fell victim to their evil ploy!
She is

Magical Girl Sunny!

No matter how much she denies it, she is Sunset Shimmer.

...unless, it's not her? But then, who is she?
---
Set in between Friendship Games and Legends of Everfree.
Edited by the ever helpful docontra.

The chapter titles do not reflect the content- it's not an anthology of anime parodies (no, really, it isn't).

This story is a sequel to The Freeport Venture

Young Kukri Doo faces the greatest crisis of her young life. Worse than the time her ship was chased by pirates. Worse than the time the Equestrian Intelligence Service took her prisoner. Even worse than the time a Primal Changeling tried to turn her into its next meal.

It's Sunset Shimmer's birthday!!! And despite being the Shimmer-mare's personal apprentice, Kukri doesn't have the first clue where to get the perfect gift for her or what that gift even is! Her parents and friends simply fail to grasp the gravity of this unfolding crisis, or the terrible consequences of failure. Who can imagine what horrors might be unleashed if Kukri can't find the perfect present before time runs out?!

Vinyl Scratch had been mute all her life. She's long since accepted that. It doesn't get in her way as much as one might think.

But, when it comes to telling Octavia how she feels, there could be no greater obstacle.

This story is a sequel to Freeport Venture: More Equal than Others

Sunset Shimmer had grand ambitions upon becoming Freeport's only magus, most importantly helping out the citizens of Freeport itself. When she hears of an outlying farming community in danger from a horde of undead, she knows she has to help them. Even if they can't pay her fees, it's the right thing to do.

However, this new challenge might be too much for her to handle. These zombies are unlike anything she's ever seen, and an old enemy is mixed up in the middle of all of this. Sunset has no idea what dark secrets the undead horde hides, or the danger posed by the necromancer behind it.