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

Lately, Discord had taken up gardening.

It was, admittedly, an unexpected hobby for the spirit of chaos and disharmony to pick up. But he'd easily justified it to himself--and everypony else who dared question--with the answer that chaos is being unexpected, and that true chaos is doing things that no one would have guessed, and so he was living perfectly up to his own nature.

He had created six unique varieties of flowers; they were completely unique to his little garden. Nowhere else in Equestria did one grow.

Many years ago, shortly before the birth of one Twilight Sparkle, Celestia, ruler of Equestria, found a small item in a forest. That item? An egg. Around the same time, in another place, Celestia, ruler of Draconica found something small in a forest. That thing? A pony.

Art(C)me
Ponies(C)hasbro
dragons(C) ?

The wheel of time turns, as destiny and history clash together.

Fifty years into the future, Sunset Shimmer is Princess Twilight Sparkle's most faithful student. She is smart and eager, but doesn't always think things through. Her life had been perfect, right up to the End of the World.

With a ruined future, Sunset travels into the past to alter the course of history. With only her mentor's cryptic word to go on, Sunset and the Elements of Harmony must solve the riddle of the Dark Regalia and stop the mysterious Vesper Radiance from rising to power. But the further Sunset goes, the more she feels like she's been through it all before.

Is destiny set in stone, or can Sunset shape her own future? Only time will tell.

Featured on Equestria Daily 6/16/13
Gratefully edited by JustAnotherTimeLord, Icarus_Gizmo, Cerulean Voice and Bad_Seed_72

The Sunset of Tropes page!

Searching for any records King Sombra may have left behind, Twilight learned of the shadowy king's tragic past. However, she also discovered his horn, in which his mind and remaining power were contained. Determined to learn how to use his Dark Magic for Good, Twilight brought Sombra back to Ponyville with her. After all, what could he possibly do as a horn? ...Or will he stay that way?

Edited by Darth Vendar and Myrkur
Inspired by Issue #1 of FIENDship is Magic
Gore tag just to be safe.

Edit 06/15/23: Now in the top 2K stories on the site, by rating! Thank you all!