When Twilight receives a letter from one claiming to be a changeling, she is shocked. As she starts reading, however, she soon learns that there is far more to it than she ever suspected.

Reading by Goombasa.

The story had been translated to Russian: Here and Here

Special thanks to PoisonClaw for editing.

For the Weekly Prompt (changelings) of the Hazardous Writing Materials and Challenges

Warning: Philosophically dark.

A lot has happened since Celestia and Luna disappeared nine hundred years ago. There are no wars, no diseases, no pain, no death. Princess Twilight, Discord, and Spike do everything to ensure that the utopia continues.

But even the most ideal paradises have ponies that wish it wasn't so.

Story inspired by Mister Saugrenu’s artwork 1000 Years in the Future.

Reading by Scribbler Productions

Edited by Soge.
French translation by Anima Draconis.

Twilight Sparkle is asked if things were things.
Then she is asked if the things they were weren't what they were.
Then she is asked if the things that weren't what were were what they weren't were.
Luckily, Discord is there to make sense of it all.

One night in her castle, the Princess of Friendship makes a startling discovery about the nature of the universe.

She tries to explain her discovery to her friends, with mixed results.

But no matter. The pursuit of knowledge must continue.

Twilight Sparkle has spent months researching chaos magic, developing a new spell to unlock magic nopony has ever experienced before. But when something goes wrong with casting, Twilight finds herself turned into a Draconequus and unable to control her new chaos magic. If she ever wants to be a pony again, there is only one who can help her learn to control her new magic.

Of course, learning from Discord was never going to be simple. And after a while, being a draconequus doesn't seem so bad anyway....

Based on the concept by Lopoddity

Editing by DB_Explorer
Proofreading by Mac349 (Ch. 1-11), Trippy998, Just A Fabulous Cat (Ch. 1-5), Doctor Candor and skysthelimit (Ch. 1-11).

Twilight Sparkle broke time when she got her cutie mark. Now Twilight and Sparkle are sisters from another time. Twilight is hailed as the potentially greatest light magician of all time, and already has a reputation as a hero by the time she goes to Ponyville. This isn't her story, not primarily.

Sparkle is an orphan - her dark magic killed her parents. She lives with her brother in Canterlot's industrial sector because they can't afford anything better. She can't leave either. She's a natural dark mage; while Sparkle won't go mad like Sombra, her reputation is hardly any better. Worse, the law doesn't see her as a good pony.

The fact that the dead don't stay dead around her, or that Thorn - Spike's double - is an undead, soul-eating abomination, are other matters altogether.

(Also has some Slice-of-Life, but fimfiction tags won't let me put it with Adventure.)

Has an ask blog to go with it: Ask Sparkle and Thorn.
Also has a TvTropes page: Split Second Tropes.

Featured on EQD.

Cover art by Swirling Line.

Helping a lost filly find her way home should have been a walk in the park for Princess Twilight Sparkle, but this time things turned out to be a bit stranger than she was expecting.

In the warmth of her cloud home, Rainbow Dash is about to turn in for the night when she hears Scootaloo crying outside in the middle of a vicious blizzard. Plucking the freezing filly from the snow, Rainbow hopes to provide some much-needed comfort for the otherwise tough young pegasus, but she uncovers a disturbing reality that she knows she cannot handle alone.

Knowing only one pony that could really help her out, Rainbow enlists Twilight’s help, determined to set things straight for Scootaloo. But what Rainbow doesn’t know is that in her efforts to provide a better life for the filly, her friendship with Twilight will develop into something more.

Edited by Alcatraz, Rated Ponystar, Rocinante, Ponysopher, Marshal Twilight, Knight of Cerebus, ShimmeringStallion, and Jake The Army Guy

Proofread by Neko Majin C

Twilight isn't having a very good day. An experimental spell blew up in her face, an army of changelings is attacking Canterlot, and she just died. Yet somehow, it looks like it's going to keep going downhill from here.

Given the chance to correct what's gone wrong, Twilight swears she's going to fix all this even if it kills her. Which it will. Frequently.

Cover art by Pixel Prism
Spanish Translation
Series TV Tropes page

When Twilight Sparkle slipped beneath the covers last night, everything had been fine. She had friends whom she loved, a teacher she adored, and a bright future ahead of her. But when she woke up, her blankets and quilts had been replaced by hospital gowns and padded restraints.

Everything is wrong and nothing makes sense; even her friends have changed. The doctors keep telling her that she is sick, that none of it was real and that it was all in her head. Yet she remembers a life far beyond the hospital walls. She couldn't have made it all up on her own. They must be lying… right?

Ask Asylum Twilight - Still updating regularly!
Equestria Daily
TVTropes
Asylum Fan Group
The Tartarus Project
Russian Translation
The Asylum 20,000 View Spectacular Stage Show!

Art:
Asylum Cover by conicer
Twilight and Twilight Smiles by dreamingnoctis
Mirror Twilight and Plague Doctor by Jaestring / BloodGoldWings
Twilight Smiles and Doctor AJ by conicer
Nurse Ratchet and Silas and What's in the mirror? by Archonix
Doctor AJ Sketch by Archonix | Colored and vectored version by ReFro82
Twilight's Asylum by Khan the Cake Lover
Smilight by HappySwitch
Twilight Waking Up by Dombrus
Fan Art by toxicdemon10
Asylum Twilight by Madness-With-Reason
Asylum Fluttershy and Asylum Ch 26 by Downburst-Backspace
Twilight and her Twin by v747
Birdgirl by sirValter

Readings and Videos:
Asylum Animated Trailer Video by formuladash
Reading by Gammarobot (SugarCubeRadio): All Chapters Here
Reading by Ender Brony: All Chapters Here
Reading by VisualPony: All Chapters Here
Reading by MelancholyIguana: All Chapters Here
Fan Trailer by Kaidan: Asylum FanFic Trailer Cuckoo's Nest

Sanctuary by Kaidan
Broadhoof Files: Dr. Humors by TypewriterError
Broadhoof Files: Corporal Phalanx Spear (Ret.) by Phalanx Spear
A Hearth's Warming Tragedy by Seven Fates

A special thanks to Breath of Plagues, Rex Ivan,
ChudoJogurt, Cynewulf, Death the Kid, Selbi, PrinceDolph, Blahman2816, Queue, and Gage!

Axan Zenith - Dr. Dreamer
Dratini4 - Way Finder
psychicscubadiver - Bright Mind
Velkaden - Dream Chaser
Reese - Silver Glow
Viola Heartstrings - Clover
Archonix - Spinney Whiteacre