This story is a sequel to Pinkie Pie Places Her Tongue on a Polar-temperature Pole

Our dear, darling Princess of dusk decides to directly defy her sister’s dangerous designs. This delivers her to a definitively undignified destiny.

Cover art by the undoubtedly dashing and debonair Yakovlev-vad.

Starlight Glimmer is rewarded with new responsibilities in the wake of her ordeal with Queen Chrysalis and the changelings ... but she can't forget her past transgressions, even if all her friends have moved on from them. Now, her past is ready to return to the forefront.

Love is one feeling that can never be taken from someone's heart. No matter how many years of separation, no matter what wrongs were done in the past, no matter how much enmity exists between two ponies, love will always stand; at least that's what Nightmare Moon is hoping for. 700 years ago was the last time she had seen her sister Celestia, and her departing words had simply been 'I love you'. Now, after so long, Nightmare Moon's heart longs for its other half; and thus, she has brought Celestia back from the far away, magically void lands she cast her to so long ago. Now, she wonders if her sister will ever find it in her heart to forgive her for what she's done, and if their lives together can ever resume as they once had.

Takes place 300 years before when Luna would have returned from her banishment to the moon, and takes place in a universe where Nightmare Moon was never banished in the first place.

TVTropes Page!
Thanks everyone for getting the story to the feature box! (12/10/16)
This is now my 1st story to have broken 200 likes! Thank you all so much!
SPOILERS IN THE COMMENTS

Some think that when you die your life flashed before your eyes. This is not what happens, for when you die you go on a walk with death and simply talk about what you have done. King Sombra is dead and is taking this walk, What will The Pale Mare have to say to Sombra?

(My first story ever that I've decided to submit So feedback would be nice.)

For the first time in over a year, Princess Flurry Heart is left alone, creating the perfect opportunity for any ol' villain to come and take her away.

Those poor bastards.

After seeing that something that wasn't quite right on Twilight's birth certificate Pinkie Pie decided to go ask her about it.

After all, it was probably only a simple mistake, right?

Edited by Jumbled, Weakest Link, Link4 and others. You guys are awesome!

Twilight gets killed protecting Princess Celestia and wakes up to the words Game Over floating in front of her.

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.

When Starlight Glimmer decided to play with time, she created worlds that never should have been. Now she goes to a young Twilight Sparkle, to give her the tools to end the war with Sombra.

She can only hope the Twilight in this world can forgive her for it.

Editing by: m1ntf4n

As I sit upon my icy pond, a young filly comes to talk to me. It's not often that I get visitors, and she's so sweet I want to show her my Garden.

And we could play and be happy there. Forever.