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

It all started with a simple question: What if? What if Luna had ponies who noticed the beautiful nights she created. Would she have turned into Nightmare Moon? Would she and Celestia rule together for a thousand years? Would Twilight meet the rest of the bearers of the elements and become friends with them? Now, with the help of a new magic spell that she created, Twilight is going to find out!

Welcome to the Lunar Republic!

Featured 4/9/15

Pandinus Imperator (You can call him Pan, he won't mind) is knocked back in time during the Canterlot Invasion, and accidentally kills King Sombra on arrival. Instead of being executed, the changeling is surprised to find himself being hailed as a hero, and is promptly put on the throne as the new monarch, the Crystal Emperor. However, Pan now faces a great many problems, among them Celestia and Luna, who seem certain that the changeling is secretly up to no good, as well as several political factions secretly plotting to undermine his reign. There's also the tiny problem of the constant snowstorm that threatens to cut the city off from the outside world permanently.
The Crystal Ponies need a hero now more than ever before. Why did they get a changeling instead?

We Has A TvTropes.

While not truly a part of Bucking Nonsense's Changeling-Verse, the same rules regarding changeling abilities and society apply.

Cover image provided by gabapple, used with permission.

When Sombra, ex-ruler of the Crystal Empire, is discovered alive and well, Twilight has her hooves full keeping the tyrannical king in check. Instead of the original plan of throwing him in a dungeon or banishing him to Tartarus, Celestia decides to go with the plan that worked out well enough for Discord.

To reform Sombra.

Pinkie takes the job, and gets right to work in helping Sombra become a better pony. Will Sombra finally change from his old, wicked ways and reform? Or will he instead strangle the annoying, pink menace known as Pinkie Pie?

Thanks to the awesomely talented Mickeymonster for letting me use his art! Check him out for even more spectacular artwork!

Three phoenixes' Burning Days occur simultaneously, against all possible odds. Deciding to take advantage of this once-in-an-eternity possibility, Philomena, Fawkes, and Ho-Oh meet in the Unbecoming realm to share experiences of their worlds: their masters, acquaintances, apocalypse aversions, and practical jokes.

A collaboration with AbstractThought. Preread by Unimpressive Vagaries. Edited by ChromeMyriad and GaryOak.

Now featured on:
Equestria Daily!
The Royal Guard's Fic Spotlight #01.
Canterlot's Finest.

This story is 100% approved by Twilight's Library!

Starburst, the daughter of Princess Twilight Sparkle and Prince Flash Sentry, has about all she could ask from life: loving parents, her Little Brother Best Friend Forever, and despite her seriousness and disciplined mentality, she has group of friends close as family. She also has an ambitious goal in life: she wants to be the first mare ever to become the Captain of the Royal Guard, which she's been preparing herself for since she was a little filly.

So... what would happen if she were to meet a pony that is an exact opposite of her?

Covert art, the universe and most of characters by kilala
Edited by Lazygamer313
Proof-read by: Zaleros, Vrilix
Former proof-readers: Merchent343, TexPony

Edited by the lovely PhiliChez

Now with a TVTropes page!

A strange blue box crash lands in the middle of the Everfree Forest to be discovered by Twilight and Spike. The Doctor stumbles out of it and makes the shocking discovery that he's accidentally traversed to another universe entirely! Ready to test his new four legs in this universe, the Doctor does what comes naturally to the renegade Time Lord; jumps cutie mark first into danger.

With Twilight Sparkle and the other Elements there to make sure he doesn't do anything too stupid, the Doctor with his TARDIS goes off to explore everything this new universe has to offer. New adventures and historical ponies await the crew as they continue to go onwards and upwards.

Cover art by: http://bakki.deviantart.com/

Brilliant isn't it? Check it out! (slightly NSFW)

During the entrance exam to Celestia's School for Gifted Unicorns, Twilight completely loses control of her magic. Celestia tries in vain to calm her down, but having no other choice she's forced to use a shrinking spell on the filly in order to tone down her dangerous surge of power.

After the exam, Celestia takes the tiny Twilight as her personal student to teach the young unicorn control over her powerful magic, making sure that she will pose no threat to other beings.

Will tiny Twilight be able to step out into a world designed for someone far larger than her? And will her size impede her in the trials of life as princess personal student ?
Side stories: "My Little Twiny April Foals Day" and "My Little Medic"

[img]https://imagizer.imageshack.us/v2/109x149q90/138/zvuu.png[/img] [img]https://imagizer.imageshack.us/v2/136x137q90/843/7m25.png[/img]

Sub-autors:
Kydois (Audience <3!)
Georg

Editors:
kingtiger666
Ultra1437
Frozen Ice King

Pre-reader:
Rated PonyStar

1000 years ago lived Starswirl the Bearded. The greatest unicorn magician at the time, and the personal student of Princess Celestia. In his study into the nature of magic, Starswirl finds a spell unlike anything the world has ever known. Unfortunately for the old unicorn, casting this spell turns his entire world upside down and sideways and brings the elements of Harmony down along with him.