This story is a sequel to Split Second

Twelve years ago, she broke time. Two alternate timelines exist, each with a different version of Twilight Sparkle. Both versions of her are able to see the other. In this timeline, Sparkle is a Necromancer.

Or rather, she was. Sparkle is dead now, not that she cares. She's got a new body. With Thorn (her undead dragon son) and Cobalt (her apprentice and an assassin for hire) at her side, she's ready to take on the world. Again.

(Spoilers in the comments. Read at your own risk.)

Featured on EQD.
The Tv Tropes page
The Ask Blog

This story is a sequel to Split Second and won't make sense without it.
This story also loosely shares continuity with Lupine Tree. Reading that is not required.

Cover art by Swirling Line.

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.

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 But when she woke up, her blankets and quilts had been replaced by hospital gowns and padded restraints.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

A recurring nightmare convinces Luna that, since her return, she has never regained her sister's complete trust. And at the forthcoming Festival of the Eclipse, she decides to make amends with a bold gesture.

But Luna's solution causes consequences she never anticipated. Consequences the whole world will feel. Now, Celestia and Luna must set forth on an adventure that will take them even into Tartarus itself, and set everything right before it's too late.

And if they're lucky, they'll rediscover the trust they once had a thousand years ago.

This story is a sequel to The Monster We Made

She betrayed us.
She mislead us.
She imposed her rule upon us.
We rose in defiance.

After the changelings' failed invasion of Canterlot, Twilight tries to soothe some of Ponyville's rampant paranoia by casting a spell to prove there are no imposters hiding in the town. But her spell leaves her in an alien body, facing a mob of angry ponies who just don't believe her when she says she is Twilight Sparkle.

Or, at least, she was Twilight Sparkle, anyway...

Featured on Equestria Daily, 2/17/13
Cover art is by the awesome and amazing Conicer

Twilight has spent the last two decades fighting against the dark forces which threaten the peaceful kingdom of Equestria. As a Royal Alicorn Princess, she has no choice in the matter. She is the greatest magician Equestria has ever known, but it has all come at a cost, both physically and mentally. She resents her friends for the happy, carefree lives they've been able to lead. Somepony will have to breach her walls of isolation and sorrow before she does something foolish.

This story is a sequel to Stardust

When Equestria’s newest member of royalty asks for aid to be offered to her friends from abroad, the best and the brightest volunteer to serve. Captain Steel Song of the Dusk Guard are immediately mobilized to help XCOM defend their world from the enemies that besiege them. However, their first joint operation with the humans takes a turn for the worse and they quickly find themselves fighting for their lives against the full force of the monsters that threaten Earth.

(Stardust/Dusk Guard crossover)
(Coverart provided by a friend of Viking ZX!)
(While familiarity with both stories isn’t required, it is recommended)
(Many thanks to Arzoo for pre-reading!)
(All screenshots can be found at XCOM.wikia.com)
(Featured on 3/13/2013. Thanks everyone!)
(Now has it's own section on TVTropes as part of the Stardust series!)

Rainbow Dash charges into Rarity's boutique and announces that she's going on a date. However, when questioned, Rainbow Dash refuses to reveal who her date is. Rarity suspects something is amiss and decides to secretly follow Dash. But what Rarity uncovers is so bizarre, she will never be able to look at her friend, or herself, the same way ever again.

'Caught' has been edited slightly. Re-read and try to spot what's changed XD

The crime rate in Canterlot was hitting an all time high, which was perfect for a young thief like Chase.

Unfortunately his fellow thieves started getting caught. And everypony knows what happens when you get caught.

You're taken to Celestia and interrogated in ways so horrible, so demeaning that the one caught is never the same again.

Chase knows this and refuses to let it happen to him.

For even if he is caught, he knows in his heart that he will never give up his life of crime. And nopony, not even Celestia herself can change that...

Right?

This story is just a bit of fun that popped up in my mind. Mostly because I wanna write Celestia in a good way for once XD

No possessiveness, no darkness, just a gentle, motherly Celestia.

I'm not sure about the tags, so if I'm missing something then tell me XD