MLP/Undertale crossover.
Not a PWNY-verse story.

Long ago, the Monsters and Humans fought a great war. The Monsters lost, and were sealed in the Underground. It would take the power of seven human souls to break the barrier that kept them imprisoned. They only had six. And so the Monsters waited and hoped, praying that another human would find their way to the Underground. Some thought the seventh soul would give their King the strength to break the barrier. Some dreamed of a human who would be their friend, and save them all...or had nightmares of one who would bring back the war.

...but nobody came.

...but somepony did.

Eons after the war, with no way to tell how much time had passed above, a tiny blue filly with wings and horn fell into the underground, calling for her Mama. None knew the poor creature's nature or origins...but her soul was powerful with magic, even more so than a human soul.

None can know what will come...of this little 'Woona'.

Cover art by Sanyo21

This story is a sequel to The Rainbow's Surprise

On the day of Fluttershy and Rainbow Dash's wedding, Princess Celestia left Twilight a message saying that she should prepare herself if something happens. The next morning, Twilight awakens to find that all of Ponyville has succumb to a blinding fog. She must now travel a monster-filled town in search for her teacher and friends and try to return Ponyville back to the way it was.

Pinkie Pie is being tormented by horrific nightmares. Unable to deal with it by herself anymore she seeks out Twilight's help, but will it have been the best decision when she finds herself alone in an abandoned, fog filled Ponyville?

Sequel: http://www.fimfiction.net/story/4676/Too-Shy-for-a-Rainbow

There have been a LOT of high-quality readings of Silent Ponyville, but this one is my personal favorite:
https://www.youtube.com/playlist?list=PLGh01rbB4o3xoSV7a6Omc-UJROXHRZ1Hv

This story is a sequel to Too Shy for a Rainbow

If you liked this fic, check out the awesome Audio Dub version of it by The Lost Narrator!:
https://www.youtube.com/playlist?list=PLnqCBZacYIwK0xcHv85Lke-xFf5V9p7R4

It's been a month since Fluttershy and Rainbow Dash started dating. Everything was going fine until Fluttershy started experiencing horrific nightmares that started keeping her up at night. Looking for answers, Rainbow Dash, Fluttershy and Pinkie Pie seek out Twilight. But when the three mares find themselves within the world of Silent Ponyville, will things turn out for the better? Or will things end in tragedy?

Sequel: http://www.fimfiction.net/story/14866/Silent-Ponyville%3A-Reunion

It is the year 2038, and the Earth is slowly being consumed by a space-borne monstrosity dubbed the Black Tide, which is using nanotechnology to remake the planet into something hideously alien.

Erin Olsen works for Project Harmonics, humanity's last-ditch effort to find a new world before the Tide can wipe them out. But when that world is found, and it turns out to be occupied, Erin will need to find the courage to face the unknown in order to save the inhabitants of both worlds.

(Many thanks to Easteu for the fantastic cover image for this story!)

Now with its own TV Tropes page

There is now a follow-up to this story: Sunflower - Side Projects
Sequel: Project Sunflower: Harmony

Luna has been plagued by nightmares since she was very young, her parents and sister are concerned when no known spell shows any sign of helping the poor filly. Suddenly however, her nightmares seem to vanish and she seems a lot more cheerful. She tells them that her new friend is keeping the nightmares at bay and teaching her new things, but they simply believe that it’s a simple imaginary friend.

But he is very much real in her dreams.

Whenever Luna falls asleep, she wakes up in her dream world where her friend, Crescent, teaches her the ancient ability of protecting the dreams of children as well as a race that has nearly been forgotten.

For his time in this world is coming to an end and Luna, his ‘Little Moon’, is to become the new guardian of dreams.

A story from Luna's childhood into adulthood, inspired by the cover art.

Thank you to Berry Punch, Bocaj518, Rainbowbob and DVAN56 for their help.
Cover art found here by dawkinsia.

A post-apocalyptic story about exploring ruins, the mistakes of another civilization, and memory.

No one must ever know,
This land where we must go,
They hoped and shared their love,
Yet death rained from above,
The scars of passing linger on,
Through empty husks and unheard songs.
Although they now live in my heart,
The truth still hurts...where do I start?-Twilight Sparkle

Coverart by this guy who is awesome. THIS GUY Also, major thanks to Luna-tic for helping me edit this sucker! Perhaps even bigger thanks to Obabscribbler who made a radio play of it. You can find that radio play HERE!

This story is a sequel to What I've Become

It is highly recommended that you read What I've Become before you read this story, since this is the second story in The Humanity Within Trilogy, and you will be lost if you just plunge into this without any preparation.

Also, this story already has a sequel: What I Am!

Things have been turning up roses for me lately. I'm no longer fighting to survive, I have people that I can turn to, and I have my face back, all because of the kindness shown to me by strangers.
But will they continue to help me once they find out what dark secrets haunt my past? Will they shun me for the evil deeds that my abductors forced me to do while I was in their service? Will they continue to protect me from the monsters that destroyed my life, once they realize what kind of monster I really am?
How does one forgive a murderer?
WOOT! Feature the day it came out! (how did that happen?) 12/1/2014
Edited by Malefactory. He is fantastic at this kind of thing!
Proofread by Cantankerous. He's freaking amazing.
Also proofread by PhiliChez.
Cover Image done by the very talented PaintSplotch! You can find his FimFic account here.
And here is his DeviantArt Account!

To save her sister and her faithful student, Celestia herself must travel into the ancient tunnels beneath the ruined castle in the Everfree Forest. She, and the guards who accompany her, must face the dark, twisting corridors. Still, what was Luna and Twilight's purpose at the old castle? Why were they unable to return of their own accord?

And what watches Celestia from beyond the light's edge?

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?