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!

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 Wily's Wittle Wub

21XX...

A dark period in the world's history. With the rise of Reploids, society was thought to enter a new golden age...until the rise of the Mavericks. Driven mad by viral infection - or simple greed and rage - these Reploids become a drastic threat to the world peace...and the conflict between them and the Maverick Hunters would tear the world apart.

However, a shining light of hope remains in Dr. Light's final creation...Megaman X. With his adopted pony daughter at his side, he shall-

Wait, what was that last part?
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Part of the PWNY-verse.

Edit: Now with cover art by sanyo21!

Dr. Albert Wily...mad genius, evil scientist, brilliant roboticist, wanted criminal, would be world conqueror, loving father... Wait, what was that last part?

When Dr. Wily wakes up one morning with a tiny unicorn inexplicably clinging to his bald head, he is more than a little flummoxed. Unknown to him, this tiny creature is about to turn his entire life upside down, worm her way into his heart...and make his dreams a reality.

Can you feel the Wub tonight? Mega Man sure will.

Part of the PWNY-verse.
Edit: Now with awesome cover art by sanyo21! How does he do such awesome artwork so fast?
Edit 2: Adorable fan art sprite by SteamingBullet!
[img]http://orig14.deviantart.net/af07/f/2015/257/9/a/vinylwily_by_steamingbullet-d99jln2.png[/img]
Edit 3: New fan art commissioned by a fan!