Shadows of our mistakes can often follow us for a long time, sometimes even manifesting as voices in our heads. Unfortunately, the voice in Luna's head is a bit more aggressive than most, and it's all the worse when it catches her off guard.
The trick with such problems though, is to not repeat the same mistakes of the past. Luna's greatest mistake was thinking she had to face it alone.

Cover art is mine. Not really sure which category tags apply?

During her entrance exam, Twilight's powers goes far out of control, leaving Celestia a shell of herself and Equestria in ruins. Now Nightmare Moon is free, but even she can't stop the Tyrant Filly. She flees through time and space, finding herself in an Equestria familiar to us but odd to her. Can the Mane Six help her stop a Twilight out of control?

Fanfiction.net link here!
Weekly featured fic in Authors Helping Authors group

TV Tropes Page, with sincere thanks to DrTempo.

Cover art from here.

It has been... four years since my return during the Summer Sun Celebration and my subsequent defeat the self same day. I woke up to find myself wandering the plane between the living and the dead, unable to cross over and unable to return and seek my vengeance on the ponies that sent me here.
Yet... I find this time here in limbo most informative as I watch the living go about their lives and I discover I can still enter the dreams of those who sleep. Their screams are some reprieve from my situation but for the fourth time I see Hearth's Warming I find myself feeling something... a feeling I can not stand as it makes me reconsider my standing and my goals.

Twilight Sparkle always loves casting spells on Nightmare Night. That is, she used to love casting spells. One mishap later, Nightmare Moon is back and Twilight can't stop the great evil from coming back. Even her banana costume won't save her this time.

This story is a sequel to Families

Third in the Nuptialverse...

Twilight Sparkle has done much for Equestria. If it weren't for her, Equestria would be destroyed three times over by now.

So what happens when she has to leave? What happens when she and Spike are forced to depart from Equestria in order to fulfill their duties? And what happens when there's still important things at home to do?

Applejack, Rarity, Pinkie Pie, Fluttershy, and Rainbow Dash now have to get along without the one who leads them. All of Equestria is counting on them. Can they do it?

AU only post-season 2, since the basic idea for this fic was created long before it aired. Events similar to season 3 have happened, all of which will be revealed. Strongly recommended you read Post Nuptials and Families first.

Cover art by Concier

This story is a sequel to Post Nuptials

In the aftermath of the wedding, Spike is bitter and avoiding everyone. Twilight's determined to find out what's bothering her charge, but she walks a very fine line when dealing with an emotionally distraught child.

Meanwhile, Rainbow Dash suspects something's wrong with Scootaloo, so she starts spending more time with her in hopes of picking the secret from her brain. As she begins to truly mentor the young filly for the first time ever, she begins to see the advantages to having a little sister.

And while all this is going on, Pinkie is struggling with some old family issues that have been brought to the surface, meaning she might have to confront her past at last.

Art by Conicer

The Changelings have been defeated and Shining Armor and Princess Cadence have said their vows, but that still leaves the Mane Six and others with the issue of the strain on their friendships. And among all the guests present at the reception, a few of them are going to be suprised with what new relationships are formed.

A live reading by Alchemystudent is available here.

This story is a sequel to When All You Have Is Memories

It has been two hundred years since Fluttershy passed on. Her dear friend Discord, however, is still as lively as he was the day they first met. Unfortunately, it hasn't been easy getting used to the fact that she is dead, and Discord is struggling to move on.

As he remembers her one day, two centuries after her passing, he is visited by another immortal. One who, much like himself, was once a force of evil who was redeemed. And one who, just like him, has lost ponies she loved to the ravages of time.

This story is a sequel to When All You Have Is Memories. Reading it is not required, though it is strongly recommended.

In addition, this story follows the events of the S3 finale, but ignores S4.

Finally, this story features Nyx from Past Sins. Nyx and past Sins belong to Pen Stroke.

As an immortal alicorn princess, Twilight Sparkle has lived for a long time. However, her friends were mortal ponies, and they eventually all died. A hundred years after they have all passed on, Twilight can only think about them, and how much they meant to her. Now that they are nothing but memories, how can she carry on?

The answers she seeks may come from a most unexpected source: another alicorn, one who once threatened to cover Equestria in eternal darkness, but whom Twilight considers a daughter. With her help, Twilight might just find that she is truly not alone.

This story takes place after the events of Magical Mystery Cure and Past Sins, which was written by Pen Stroke. Nyx and Past Sins belong to Pen Stroke.

Also, check out this CinemaSins-Style review.

Celestia finds herself sharing company and her booze stash with Luna's crazed split-personality, Nightmare-Moon. However, as the night wears on, she finds she may actually be able to tolerate the dark alicorn. Maybe even like her.

For Nightmare Moon is the best pony: Contest numero uno.