On a dark night filled with sparkly magic, a group of unidentified enthusiasts of some sort attempt to give Nightmare Moon some sizzle, utterly separate from Princess Luna. But, when the spell is interrupted by Celestia's slav... guards, something totally expected is created.

Now, a little black alicorn filly named Nyx finds herself held captive by Twilight Sparkle, only to be haunted by memories and emotions from her past. Is she Nightmare Moon reborn or is she simply a science experiment? Can Twilight Sparkle protect Nyx from those who would call her out on fillynapping?
Or, will Nyx be forced to inherit the poor fashion sense that may not even be hers and become the greatest evil Equestria has ever known?

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.

An ageing pony decides to take matter into his own hooves as he tries to bring forth dawn to Equestria once more. He is met with more than he bargained for though when dealing with an angry princess and a near crippling fear of darkness.

On a dark night filled with even darker magics, an insane cult attempts to give Nightmare Moon a body and life of her own, utterly separate from Princess Luna. But, when the spell is interrupted by Celestia, something unexpected is created.

Now, a little black alicorn filly named Nyx finds herself living under the care of Twilight Sparkle, only to be haunted by memories and emotions from her past. Is she Nightmare Moon reborn or is she simply a doppelganger with a soul and mind of her own? Can Twilight Sparkle protect Nyx from those who refuse to see past her dragon eyes and black coat?

Or, will Nyx be forced to inherit the sins that may not even be hers and become the greatest evil Equestria has ever known?

I wasn't always evil. There was a time, long ago, when I was known across Equestria as the Guardian of Harmony. So what changed? Oh, nothing changed, really. The... conditions... were always there. What are these conditions, you ask? Well, for one, I'm unstable. I am also schizophrenic. And I have Dissociative Identity Disorder (Once called Multiple Identity Disorder). It all just... took a long time to reveal itself. And when it did? When I finally snapped? Nothing had ever felt more liberating... or more painful... in my entire life. I began to hurt my loved ones. I began... to kill. I am Discord, and this is my story.

(Side-Story of One Soldier's Twilight )
Something goes wrong with Twilight's teleportation to Earth and Rarity finds herself in a predicament, alone in the Siberia in the dead of winter. Finding refuge in the cabin of a hermit, she hopes to enlist his help to get to Twilight and then back home before the cold of both his heart and Siberia keep her from getting home.

Chrysalis is dying, and with her, the last of the Changeling race... but there might be a way to avoid extinction.

An ordinary week for Zecora gets turned into something special when a foalhood friend from the Savanna abruptly decides to move to Ponyville. The week then becomes something stranger when she learns a secret he had been keeping from her since before she left; and it gets weirder when she meets his bizarre "Beloved". Zecora feels that she can handle this, but can Ponyville?

Rated teen for some mild gore and carnivore culture in some later chapters and for mild sexual themes including inter-special relationships.

Getting a college roommate is random chance.
Sometimes you get lucky, and sometimes you get a pony.

Rainbow Dash enrolls at an Earth university.

Update: and then some other stuff happens.

Sam wakes up in Equestria stark naked and with no clue how he got there. More problematically, he seems to be in somepony's home.

Teen for nudity and the awkward situations arising from said nudity.

A rewrite of Make Friends, or Die! by Sam Polson (which has since been taken down). I liked the premise, but Sam's English was spotty and Google Translate didn't help him much. Starts going in its own direction fairly quickly.