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

One Piece X MLP Crossover

A emergency trip to Zecora's leads Fluttershy to find a strange pony with a straw hat. Unfortunately, he scares Fluttershy off with his talk of eating other animals. The strange pony's arrival in Equestria sets off a chain of events that threaten plunge the peaceful kingdom into an all out war. Twilight and her friends, along with the new pony may be the only ones who can unravel the mysteries that surround Equestria and save it from falling apart.

Now with TV Tropes!

New Cover Art by Droll3

Princess Twilight Sparkle is perfectly happy with her perfectly ordinary life in Ponyville. Every library book is properly shelved in its appropriate place, and her life continues on exactly according to her meticulously planned out schedule.

Then she gets a bodyguard.

Now she has to find some way to fit this new pony into her life on short notice. It won’t be an easy thing to adjust to—especially since Captain Storm Kicker’s presence makes it that much harder for her to go on living like the same old Twilight Sparkle she was before she became a princess.

Megan Richards is a normal, everyday wife and published author of 'My Little Horsey'... however the tales she writes about aren't fiction, but stories from her past. She thought she put the world of ponies behind her, but sometimes the past has a habit of catching up with you...

G1 meets G4 in a hopefully epic tale of the past, the present and the future.

I own nothing, also, minor cameos from other Hasbro properties such as Jem and the Holograms, Transformers G1 and GI Joe.

Cover image made by the very talented Egophiliac and from here.

fanfiction.net link!
Equestria Daily link... one of these days.
TV Tropes page
All the Tropes page

Sequel: The Conversion Bureau: United We Stand

Side-stories and mini-arcs not able to fit into the main narrative: Side Stories of First Contact

If there's one thing we can count on, it's Twilight Sparkle, prized student and newest princess, to botch up a spell in her quest to master all of magic.

This time, it propels her to a new world, this one not inhabited by bipeds, but ponies like herself, and yet not like herself. She has entered the realm of Everglow, where the queen is a queen, and ponies suffer horribly lethal combat much more often than Equestria could manage under the peaceful reign of its alicorn caretakers.

Will she find her way back home, to her friends and responsibilities? Will she survive the harsh new realm she has entered?

Based on Ponyfinder. Want to support the author? Check out his Patreon.