When Dipper and Mabel Pines stumbled upon that ancient looking machine in the woods of Gravity Falls, they had no idea what it would do. So like any other people idiots would do, they got in.

Discord isn't just a creature of chaos, he is chaos. Holding back such lawless magic may just be the end of him.

"And here you'll see the statue of the Lord of Chaos, Discord, imprisoned in stone..."

A group of students from the School for Gifted Unicorns are given a chance to visit Celestia's royal garden and a curious filly decides to ask about a statue that's in their tour, where they all hear the story of how the spirit of chaos fell into a stone imprisonment for the third and final time.

Art by: Kabudragon

(Rewritting) In a quiet little mountain town in Colorado, an elementary school is taking a field trip. When a few of them wonder off, they discover something that takes them to a new world. Equestria. In the evilest of all places, Stan, Kyle, Kenny, Cartman, and Butters must find a way back, or literally die of boredom. (T, Contains a bit of bad language and references. Read at own risk XD)
[Crappy Cover Art belongs to me]

Rainbow Dash has a freak accident while performing a Sonic Rainboom, and awakens to find herself in a strange new world, with strange new abilities.

Avengers and My Little Pony crossover.

Image Credit goes to Alienfirst : Link

Nightmare Moon wasn't sent to the moon instead she's in a insane world whose inhabitants were bipedal. They were in trouble on the brink of war. Nightmare had just been in a war, she knew they needed her help. But, which they would she help? Is it possible? Could Nightmare ever be one of the good guys?

Discord's the only creature in Equestria who can recognize the human for what he is -- not the long-lost Seventh Element that never actually existed and couldn't have existed before the human arrived, but a meta-reality warper, an entity far more powerful than Discord with the power to warp the minds of all around him and the very rules of magic to make sure that he's always the Big Hero. And the role the human's assigned to Discord is the Villain to beat down or kill.

Pre-reform Discord's fine with being the villain. But on his own terms. Not dancing on some alien interloper's puppet strings.

Without friendship, or even allies, Discord's going to have to find a way to defeat a creature who can alter fate itself and who can even mind-control him. Or he may just end up worse than dead.

Art by Tenchi-Outsuno. Progress Bar at my writing journal.

Trigger warnings: Mind control (magically induced love, magically induced friendship, magically induced stupidity, Discord being Discord), noncon/dubcon (magically induced love, other forms of highly dubious consent), rape (female on male), violence/gore (mostly against Discord), literally everything in chapters 19-21, humans not being presented as unilaterally wonderful and superior to ponies and/or draconequui.

Everybody thought the Elements of Harmony kept us safe from the evil things waitin' to come for us in th' dark of night. It happened so fast, that before Ah knew it, th' world I knew was gone. All Ah left... all we had left, were each other. They thought they could put our kind in chains. They thought we would all bow our head to their Queen.

We're th' Crusaders. And we don't bow.

We fight.

Jack Frost, the newest member of the Guardians, vanishes into an unknown world, devoid of all but the most basic of his powers.

Pitch Black, the Boogy Man, falls through time and space to escape the ever pursuing darkness, and finds himself on a strange world with Jack, his old enemy.

Together they form a truce to find out more about the land and, unknowingly, form a bond of friendship thought to be impossible.

~~

Crossover with Rise of the Guardians movie by Dreamworks

Discord, after Tirek has gone back to his prison, has trouble dealing with his own inner demons. He knows what he did. He knows what he did was wrong. Unable to cope, he does the unthinkable.

He loses his mind.

Now, once things seem right again, Twilight is sent on a quest to discover what really happened to Discord, and moreso, how to save him from his worst enemy. With unexpected aid from unknown forces and a mystery to solve, will they be able to save the day in time? Or will all fall to Chaos?