Pandinus Imperator (You can call him Pan, he won't mind) is knocked back in time during the Canterlot Invasion, and accidentally kills King Sombra on arrival. Instead of being executed, the changeling is surprised to find himself being hailed as a hero, and is promptly put on the throne as the new monarch, the Crystal Emperor. However, Pan now faces a great many problems, among them Celestia and Luna, who seem certain that the changeling is secretly up to no good, as well as several political factions secretly plotting to undermine his reign. There's also the tiny problem of the constant snowstorm that threatens to cut the city off from the outside world permanently.
The Crystal Ponies need a hero now more than ever before. Why did they get a changeling instead?

We Has A TvTropes.

While not truly a part of Bucking Nonsense's Changeling-Verse, the same rules regarding changeling abilities and society apply.

Cover image provided by gabapple, used with permission.

While on a trip to Canterlot to do some research, Twilight happens upon a dust-covered book titled Insane Edicts: A Legal History of Equestria. Sure, the book seem innocuous enough, but when she opens it up she discovers that Celestia is far more eccentric than she'd like to believe.

Sequel to Let the Silence Sing!
Big Macintosh is dating Princess Celestia, and now all of Equestria knows thanks to a certain foal photographer. Dating a Princess is hard, thanks to her demanding schedule and his work at Sweet Apple Acres. The two rarely speak to one another during their get-togethers, but the silence sings between them.

Celestia decides that Big Mac's barn is an excellent place to sneak off to, to take naps on her days off.
Big Mac decides that Celestia is a welcome guest.
Neither Princess nor farmer ever speak to one another, but the silence sings between them.
(Cover art by GrapeParfait!)

Hope is the faith of the young. Losing everything she holds dear, Puppysmiles embarks on the adventure of her life to find her mother, her hopes of meeting her again driving her through the horrors of a world not of her making. Too bad the Wastelands doesn't care about hope.

This story is a sequel to Stardust

Times are changing for Equestria as Twilight’s return brings with it news of people and cultures from beyond the peaceful world everypony knows. Aid and volunteers are freely offered to help the besieged humans of Earth because every Equestrian knows that’s what good friends do. Unfortunately, making friends can also have the unintended consequence of making enemies.

When the monsters besieging the humans strike at Equestria with a level of brutality not seen in over a thousand years, the cry for help is sent to all the kingdoms of the world. Honored allies step forth to fulfill ancient treaties and oaths. Enemies, old and new, bury their grievances. An alliance never before seen in Equestria will be created to combat the monsters from the void.

And because of these events, a grim but welcome sibling to the XCOM project is born.

(XCOM/FiM Crossover)
(Sequel to Stardust, which I recommend reading before starting this. Fortitude Amicitia and Broken aren't required reading but are supplemental to the storyline)
(Gore tag for blood and violence)
(Alternate Universe tag because of the divergence from canon that Stardust has caused)
(Uses elements of Season 4)
(Coverart produced by the amazing Carnelian!)
(Many thanks to Arzoo, BradTheBrony, Vandenbz and Setokaiva for prereading!)
(As of 03/07/2016, the prereading team consists of Arzoo, BradTheBrony, Noble Cause and Metallusionsismagic!)
(Complete with it's own TVTropes page as part of the Stardust continuity. Could use some updating!)
(Character tags will be added as chapters are added!)
(Featured 5/12/2014! Thanks folks!)
(Possible spoilers in the comments! BEWARE!)

Tirek has won, and Twilight's friends are gone. She and the other princesses have just one chance left. Maybe if one of them can go back, she can warn them right when he escapes and stop this all from happening.

It might be a long shot, but it's the only chance they have left.

Set just before the events of chapter ten of Friendship is Optimal. One of the last living humans survives and scrapes by in the ruins of Eugene Oregon. He is approached by a simulacra of Twilight Sparkle, who promptly attempts to convince him to upload himself to Equestria. He balks at first, so Twilight plays to her strengths: studying.

Part of the Optimalverse.

WARNING: RATED TEEN FOR IDEOLOGY. This story attempts to take a realistic and balanced view of why an intelligent and religious person might not upload. It does not attempt to convince the reader to believe any of the viewpoints discussed. However, it is written in as unbiased a way as possible, therefore, both theists and atheists will probably find portions of it offensive.

There was only one explanation. For all of it. All of the strange, erratic behavior. Her irrational fear of the sun. Her nocturnal habits of locking herself in in the dark and closing all the blinds. Wearing her sunglasses everywhere, even inside! It was time to invest in some silver, garlic, and a wooden stake.

Big Macintosh becomes host to the will of an ancient eldritch necromancer.

Nothing changes.

Written for EQD's Writer's Training Grounds #017.

(Audio version by AppleCore.)