Brought to you by Loyal2Luna, this new Downloadable Content for Mass Effect 2 brings the fight to Equestria.

Just about ready to embark on their mission to stop the Collectors from further abducting human colonies, Commander Shepard and the crew of the Normandy SR-2 are given a new priority, when the Illusive Man tasks them with investigating the mysterious disappearance of a Cerberus science team.

Soon, what begins as a simple search-and-rescue unveils a mystery millions of years in the making, and the Commander finds himself thrust into a situation he couldn't possibly have prepared himself for.

Join the Hero of the Citadel as he uncovers the secrets, combats the demons, and ultimately decides the fate of the impossible world known as "Equestria."

This story is a sequel to Rider on the Storm

For the briefest of moments, Anonymous wielded absolute power. He single-handedly destroyed the city of Canterlot, laid waste to Ponyville, decimated the Everfree Forest, and came dangerously close to annihilating the very Tree of Harmony itself. And he had an absolutely fantastic time doing it.
Right up until he lost.
Now he's stuck as a statue under the watch of the princesses he tried to subjugate, awaiting the time he'll be locked away forever, with the key no doubt thrown into a volcano. But from the very beginning, Anonymous suspected that the shenanigans of the good guys would cost him his victory at the last moment, and so he laid plans with his most loyal of subjects—all former soldiers of the Storm King he betrayed to obtain his power—to arrange for his release should the opportunity arise.
Unfortunately, he wasn't counting on the ponies calling in help from a faraway land. Enter the Four Princes of Zebrica, all wielding the same exact power that Anonymous did, and knowing a thing or two about how to put bad apples like him away for good. This is made even worse by the sorry state of Anonymous's storm beast forces, having hit hard times in the months since his defeat.
But not all is lost for the petrified supervillain. Because in a rare twist of luck, the Princes just so happen to unknowingly bring with them a zebra criminal with his own dirty little secret. A secret that not only secures Anonymous's release from captivity, but just might be the start of a horrifying new partnership, and with it, the birth of a new force of evil.
And of course, with all that going on, there's always the matter of the nascent Legion of Doom, plotting to bring their own age of darkness to Equestria as well...

Takes place during the final two seasons of Friendship Is Magic. With a few alterations here and there, because I HATE THE ANTI-FIM I HATE THE ANTI-FIM :bread:
Reading Rider on the Storm is strongly advised if you want any idea of what the hell is happening in this story.

A thousand years ago in Equestria, Luna's frustration and desperation has been building for years and years as her social and political isolation grows, but just before Luna's jealousy and resentment can turn into murderous hatred against her sister, a new event triggars Luna's mental collapse and pushes her over the edge. When Luna by circumstance finds herself alone in Celestia's room she reads her sister's diary out of curiosity and discovers all of the disparaging criticism that Celestia has leveled at her over the years about how much of a nuisance Luna has been to her, but has been too polite to say directly to Luna's face.

Luna and Celestia had always supported and stuck with each other all their lives. Even when the common-ponies critisism and shunning of her was at its worst, the knowledge that her sister loved her kept Luna going. The realization that nopony, not even her own sister valued her or thought she was fit for the throne completely shattered whatever remained of her fragile psyche.

And so Luna just gave up...

She gave in...

If no one wanted her there...

Then she wouldn't stay there...

She would leave.

Sunset Shimmer fled from Equestria in search of the destiny that Celestia sought to deny to her. She dreamed of finding great glory and power in a strange new world. But she emerged on the other side of the mirror in a harsh cruel world beset by demons and troubled by division, conflict and racial animus: the world of Remnant.

Now, years later, Sunset has completed her studies at Canterlot Combat School and is ready to attend Beacon Academy. She hopes that in the more progressive Kingdom of Vale her appearance as a pony faunus will not be held against her the way it was in Atlas, and she can rise as high as her talents permit and seize with both hands the destiny she still yearns for.

Sunset finds herself assigned to lead three fellow freshman at the Huntsman Academy: Jaune Arc, who dreams of becoming a hero elevated above all others; Pyrrha Nikos, a peerless warrior who has everything that Sunset wants and hates everything about it; and Ruby Rose, a simpler and more honest soul who simply wants to save as many people as she can, and who might just light the way to their salvation.

Together they are Team SAPR, and together they are plunged into a world of mysteries, magic, allies and enemies, robot girls and Atlasian black ops experiments. It won't be easy, but if they can work together, teach Jaune how to fight and maybe learn to get along as friends along the way, then they might just save the world.

Original Cover Art by Mix-Up
Current Cover Art by MRK50
Now with a TV Tropes page

Also with a Discord Server