The planet of Chikyu is pretty odd, from an outsider perspective. There are anthromorphic sapients of every stripe and sort, the world president is a dog, its greatest warriors are alien monkeys, the average IQ (outside genius scientists or children) is somewhere below 50, and magic orbs raise the dead. How much difference would adding a pony that barely talks really make?
...quite a lot, apparently. Just ask Mr. Popo...if you dare.
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Dragon Ball Z Abridged crossover
Edit: Cover art by CaioCoia.
On DA: https://www.deviantart.com/caiocoia

Captain Flowers thought it would be just another ordinary day. Be there for his men, keep the fighting to a minimum, and make sure nothing bad whatsoever happened to Church. Just like any other day in Bloodgulch.
And then the little pony appeared and refused to let go of his charge. This was going to be interesting...

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Part of the PWNY-verse.

Another side of the story is being written by cyberlord4444, and can be found here: https://www.fimfiction.net/story/386172/rock-in-the-gulch-analysis-anarchy

Edit: New Cover Art by ProfessorCatPro
Edit 2: Fan art by Cookie_Girl! So adorable!

His father missing, presumed dead...betrayed by a friend.
Lost and alone, Fox McCloud turns to the universe for some sign there's something worth fighting for.
The universe answers in the form of a firebrand from another dimension.
Now his life is turned upside down for the second of many times. Especially when the little filly starts calling him 'Dad'.

Part of the PWNY-verse.

Edit: Awesome new cover art by ProfessorCatPro! Along with ideas for tech pictured in the cover, which will appear in the story.

Red Team had been given an assignment. It wasn't the usual sort of assignment. They were assigned to defend their base 'until further notice'...and then never received notice. All announcements sounded pre-recorded, and enemy assaults were few and far between. The enforced inactivity was slowly fraying the bonds of the team...

...until something unexpected arrived. A tiny creature appears one day in their fortress, in need of compassion and care. Somehow, she finds that in this group of strange individuals, as she becomes their baby.

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Crossover with Team Fortress 2.
Part of the PWNY-verse.

Edit: Since I get these comments a lot, I will say here, I've never played the game and don't intend to include much in the way of game mechanics, so please don't suggest such things.

Edit 2: FAN ART! for chapter 9 by G_Haze. Makes me so happy.
Edit 3: More fan art from G_Haze, This guy's amazing!
Edit 4: New fan art! by The Pyromanecer. Thanks so much!
Edit 5: More fan art by shiningkord98.
Edit 6: New Fan Art by The Pyromancer
Edit 6: More awesome fan art from G_Haze! So awesome!
Edit 7: New fan art by Pioneering Author

When Wreck-it-Ralph finds a villain character who seems to have gone Turbo, he finds more than a handful in the handful sized sprite.
For one thing, she has no idea what game she comes from.
For another, her code seems completely foreign to the Arcade.
For a third...she's absolutely adorable.
Having only just finished cleaning up after King Candy's mess, this little Nightmare could be a problem...or the greatest blessing Ralph has ever received.
And shadows from the past move behind the scenes...

Part of the PWNY-verse.

Edit: Now with cover art by KittyCoverArt.
Edit: Now with fan art at the end of the first chapter.

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

He was an alien raised by humans, torn between two worlds and belonging to neither. His efforts thwarted, he found himself descending into madness, destined to be consumed by the nightmare he was becoming.

She was a loner, withdrawn and anti-social. When one whose regard she valued above all others turned away, she sank into darkness and despair. The madness waited.

The madness drove him to decide that if the world could not accept his enlightenment, it would suffer his madness.

The madness drove her to decide that if the world had no place for her, then it could do without her.

Sometimes, it takes another broken soul to help put your pieces back together.

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Part of the PWNY-verse.

Edit: Cover art by Sanyo21, commissioned by Level Dasher
Edit 2: Since everyone keeps asking, this is a crossover with the 'Mother' game series. Look it up.