Like ponies, changelings can get pretty paranoid at times. After all, it's not every day that a changeling gets kicked out of the hive for being a pony.

Beneath his black, chitinous exterior, cold blue eyes, and fang-toothed grin, Thorax holds a dark secret. He knows better than anyone that the best way to hide a changeling is with another changeling, but that's pointless, right? He's already a changeling.

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!)

One day Princess Twilight starts getting letters from a filly named Sunny Skies. Dealing with her paranoia, OCD, "Princess Chores" and just simple worrying, how is Twilight supposed to help a young filly make friends? And when the letters start to worry her, how will Twilight cope as she investigates into a darker side of Equestrian society.

Princess Celestia writes a letter to her favorite student, highlighting the need for proper lab safety.

Apologies to Tired Old Man. Not connected in any way to his body of work-- I just went with the pun.

This story is a sequel to Deep Cover

Butter Up isn't Fluttershy -- but she does play her on TV.

One ordinary mare. One never-ending time loop. Infinite ways to die.

How long before she snaps?

Nightmare Moon won. She defeated Celestia, broke the Elements, banished the sun. This all happened a very long time ago. So long ago, that she has had plenty of time to change her mind.

Of course, fixing our mistakes is never so simple, and never without consequences. Even with particularly potent help.

"If you came to conquer, you'll be king for a day. / But you too will deteriorate and quickly fade away."
— "No Control" by Bad Religion

A big thanks to Craine, Sorren, and Idylia for prereading and editing. If you enjoyed the story, don't forget to check out their pages.

Equestria Daily
Royal Canterlot Library (FIMfic version)
Russian translation by Doof
Chinese translation by Dreams Set Free

Kitsune Heart has done a dramatic reading of this story! Find it over here.
ObabScribbler has done a dramatic reading of this story! It includes a full cast of voice actors. Find it over here.

Comments contain spoilers.

There are many stories where Twilight tells off her friends after the Wedding. But that's not really Twilight's bag, she gets worried she's failed, or depressed, not angry. So here is a different bridal path, one where Twilight acts decisively to try and redeem herself in the eyes of her friends and sovereign, and ends up travelling to places she never imagined, facing dangers and foes she never dreamed of and making even stranger friends. Of course, there is still a 'reason you suck' speech delivered, but delivered by the last person anyone would expect...

Twilight was always fated to be the savior of Equestria, along with her friends. But fate can be so easily altered. What happens in one alternate realm when instead of marrying a unicorn, Twilight's mother had instead married an earth pony, resulting in her daughter being hornless? Without her magic, Twilight's future and destiny are far less certain, as is the destiny of all of Equestria.

However, destiny is not so easily set off course. When the princess of the night returns, can one little earth pony hope to be the one to help her damaged heart?

Now with a TV tropes page! Thanks to redandready45.