After the Changeling invasion, Celestia and Luna make the decision to have Twilight investigate the Elements of Harmony and solve the mystery of their power.

A thousand years later, Rainbow Dash awakens in a world she does not recognize. She has no idea how or why she came to be there. She does not know the language, the geography or any of the rules of this new time. She soon finds allies in Star Fall, a scholarly pegasus whose Talent is Magic, and Astrid, Star Fall's Griffin guardian. Together they set out to discover why Dash has been sent to the future, and how she might return to when she belongs.

War threatens the nations, a Nightmare stalks the shadows, and Rainbow Dash's arrival has turned her into a wild card in a deadly game that pits the law on both sides of a broken Equestria against a mysterious criminal figure, Max Cash. Yet the stakes are higher than anyone knows, for in her research Twilight Sparkle discovered a dark secret about the Elements, something that will shake the foundations of the world.

Cover image by SierraEx
Has a TvTropes page

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!)

This story is a sequel to What Comes Next

Author's Note: Although this story is a sequel to 'What Comes Next,' it functions solidly as a standalone feature, and an excellent entry point into the 'What Things May Come' Trilogy. It does, however, feature prominent spoilers from the first story.

Ponyville works to rebuild after a devastating attack leaves much of its infrastructure battered and broken, but even as the town pulls itself back together, it soon becomes clear that not all is well. A dangerous, mysterious, and seemingly omnipresent foe emerges from Pinkie's worst nightmares, and may be to blame for the disappearance of Ponyville's own. As Canterlot scrambles to understand this new enemy, the Mane 6 find their Elements - perhaps even their very souls - under attack. Time, however, is not on their side, and every moment spent preparing for the upcoming conflict may very well cost the ponies of Equestria dearly.

This story is a sequel to Project: Sunflower

After the events of Project: Sunflower, Erin Olsen has returned to Ponyville, happy to pursue her studies in magic. After everything that happened the year before, she's looking forward to spending her days studying and having fun with her friends.

Meanwhile, on the newly discovered world of Harmony, humans and ponies work together to study this strange new world. However, their arrival causes something ancient to begin stirring. Something that may end up changing everything.

Erin will need all of her courage, all of her cleverness and, of course, all of her friends to see herself through what happens next.

Cover art by Valkyrie-Girl
Editing provided by:
Brilliant Point, Coandco, Ekevoo, Ludicrous Lycan, Merlos the Mad and Razalon the Lizardman.