Celestia has a dangerous creature held in the deepest of Canterlot's high-security dungeons. It can create ponies (with full backgrounds and histories) with it's strange and often-times prophetic powers. The Princess does her best to keep it under wraps, but its only a matter of time before it's "creativity" will get out of control.

[Breath of Fire III x MLP]

He was supposed to be going at a costume party, dragged away from his house by his closest friends. Being the typical anti-social teen who did not want to socialize, he came begrudgingly after he heard that the theme was supposed to be about your favorite video game character.

It was only after he bought a replica of a perfectly completed boxed set of his favorite character's Dragon Genes-- marble-like objects that hold spirits of slain dragons which the character can then use their power after finding them-- that everything went wrong.

On the night of the party, when the authentic looking diary that came along with the box opened suddenly without anyone touching it, he made the mistake of coming close to it as the pages began to rapidly turn on their own.

Now here he was, in an different land where his anti-social lifestyle was finally biting him in the rear, his body turned into that of the character that he was planning to dress up as, and no idea of how to get home. What left is there to do other than brood?

I always wanted to go to Equestria. When I got the chance, I took the deal without reading the fine print. To my surprise, I didn't arrive there as a pony, or even as a human. It seems I get to view this world from a different perspective than what I've imagined.

My name is Echo. I am a Diamond Dog.

-Edited by the one, the only, Nathan Traveler!
-(Cover by Jovial_Shake of fimfiction.net)
-Now featured on Equestriadaily.com!

The Conversion Bureau never made any sense anyway, but here are some places where it would have made less sense.
Not necessarily worlds where the ponies would lose the fight - just worlds where conversion wouldn't logically work.

Before suggesting a World, read the index to make sure I haven't done it already.

When the ponies came, they tried to convert humanity with words and kindness, saying that they were misguided beings and the princesses would help them on the path to Harmony. When that failed, the ponies tried the potion, only for it's magic to be countered by humanity's science. Then they tried force and failed completely at that.
Finally they decided to let the Barrier defeat humanity and it seemed to work! Nearly 50% of the planet was covered with humanity doing it's best to find a solution.
Unfortunately, the ponies of Equestria are about to learn a harsh lesson that humanity learnt long ago. The Earth can be paradise for those who tame it, but to others it is hell.

Equestria is expanding unstoppably. The Conversion Bureaus are working at peak capacity. It looks absolutely certain that Celestia will replace humanity with ponies.

But then one niggling flaw appears in her plan. You see, humanity's religions, while dismissed by Celestia as just more evidence of human barbarism, are correct in at least one respect. Humanity has a loving father, and what Celestia is doing makes Him angry. So angry in fact, He's going to do what He hasn't done since ancient times: smite.

Seems like Exodus is being reenacted, and guess who's playing Pharoah?

The war has gone on for far too long. To end it, Celestia just has to sign the treaty.

Go read the comments. They're way more interesting than the story itself.

Now with an audio version
Now translated into Russian and with an audio version.

Twilight Sparkle still thinks Earth, and Humanity in general, can be classified in black and white. A visit to two different, but very similar Normandy war cemeteries might help.

She also hasn't gotten around to reading up on our history yet.

Or so Tucker, international reporter and the first human to come in contact with Equestria, thinks. Hopefully she won't hate his species by the end of this.

After a tragic accident, a human ends up in Lord Tirek's body, as part of an attempt to reform the villain after his recent escapades. While the hero of our tale is trying to make sense of his new surroundings, the rest of Equestria thinks that the most terrible threat that their world has ever seen is back...
And the powers that be are definitely not happy about it.
New Cover Art By Shadow Bolt

An accident in the lab sends our favorite boy genius to Equestria, as a pony. What will he do and how will he get back? The answer: Science! (Cover Art Updated!)
New FAQ! and TV Tropes!
Planned Phrases from Dexter:
“Pinkie Pie! Don’t push that Button!” /to Pinkie
“Please, Magic is the word simpletons and the ignorant use to describe what they cannot understand.”/ to Twilight
“No, I didn't strap a rocket to you. I strapped you to a rocket.” /to Rainbow Dash
“Friends? Who needs friends?”

Dexter is a boy super-genius with a disdain for anything girlish and no desire for friendship. After an mishap in his lab, he gets stuck in Equestria. How will he cope with the over-friendly ponies, and the girlish everything?
For any who do not know Dexter's Lab: http://en.wikipedia.org/wiki/Dexter's_Laboratory
[RIP Christine Cavanaugh: 8/16/63-12/22/2014] - Dexter's Original Voice Actress