There are two very important things to remember when you cross realities:

1) Every living thing that sets foot in Equestria gets magic if it doesn't have it already.
2) There are three pounds of bacteria living on and in the human body.

Everything goes exactly as expected when two alien cultures meet.

This is a fic based on the Time Loop Files, the format of which was first codified by Innortal on fanfiction.net.
Here's a brief guide.
The basic idea is, one character (the Anchor, usually the main character of a fictional setting) is looping back to the very first moments of their parent series every time either they die or some kind of time limit expires. They of course end up monumentally stir crazy given enough time.
Eventually others start to loop as well.
The reset is not always perfect. Sometimes a loop's history will be different to the "prime" loop, or canonical plot.
"Crossover" or "Fusion" loops also occur, randomly. These can involve the home loopers having a guest, or the anchor for one universe spending time in another, or replacements of one character by another.
Vacation Loops are where the Anchor (or others) decide/s "buck it" and lets off steam by doing whatever comes to mind. There's little or no attempt to maintain the original timeline.

In addition, and particularly more recently, it should be known that this story has a collaborative element to it - people may submit loop ideas or loops, ideally at the Spacebattles thread (a link to the current version of which is on the Trope page), and they may become included.

There's two page image options, thanks to Filraen - the current page image has been edited by the original creator from this work of theirs.. The other one is here:
http://hourglass-vectors.deviantart.com/art/MLP-Loops-466030169

Do you ever regret things you did in the past? Whether it was accidentally insulting someone, or waging war against a concept with chocolate rain and licorice trees? Well, Discord doesn’t “regret” it, but he can admit he made a mistake or two.

But his past certainly disagrees.

Audio Readings.
Read by StraightToThePointStudio
Read by Pony&Wolf Productions

Once upon a time there was a very lazy dragon who did not want to find a town to pillage.

So he decided to make one of his own.

Editors: Mitch H, Dlafrferg
Jake the Army Guy has done an amazing reading of this on YouTube
Excellent cover picture credit: Harwick on Fimfiction or Harwicks-art on Deviantart.com
Also, the Audio Project has done a reading of this and other stories on YouTube

Twilight Sparkle accomplished something incredible, something not even the great Starswirl could manage. But ascension into the ranks of Equestria's princesses is not without its difficulties. Before she can take her place as princess of Friendship, Twilight must travel to the underworld and make a ceremonial offering to Death in exchange for her immortality. Twilight is more than a little surprised to discover the identity of the pony under the hood.

After years living in Ponyville and getting to know her friends, Twilight always assumed they were exactly what they seemed: a group of friendly and ambitious ponies. But as it turns out, the sort of pony who saves Equestria and decodes the ancient mysteries of Starswirl is likely to attract ponies a tad more interesting.

Updates on the 3rd or 4th Friday of every month, then daily until that section is complete.

Editing by Two Bit and Sparktail. Cover by Zutcha.

The Canterlot Exchange, ten thousand humans and ponies pass through its doors every day, on their way to destinations all across Earth and throughout Equestria. Some are wide eyed migrants, others are only passing through, or on their way to find the most exotic holiday of their lives. They are mavericks, heroes or just everyday travellers, but every one has a story to tell. These are just a few of the tales I've gathered from the Canterlot Exchange.

With thanks to Luna-tic Scientist, Lord of Dorkness and docontra for their help pre-reading.

Winner of the Transformation group 3000 Member Celebration Contest!

Twilight Sparkle broke time when she got her cutie mark. Now Twilight and Sparkle are sisters from another time. Twilight is hailed as the potentially greatest light magician of all time, and already has a reputation as a hero by the time she goes to Ponyville. This isn't her story, not primarily.

Sparkle is an orphan - her dark magic killed her parents. She lives with her brother in Canterlot's industrial sector because they can't afford anything better. She can't leave either. She's a natural dark mage; while Sparkle won't go mad like Sombra, her reputation is hardly any better. Worse, the law doesn't see her as a good pony.

The fact that the dead don't stay dead around her, or that Thorn - Spike's double - is an undead, soul-eating abomination, are other matters altogether.

(Also has some Slice-of-Life, but fimfiction tags won't let me put it with Adventure.)

Has an ask blog to go with it: Ask Sparkle and Thorn.
Also has a TvTropes page: Split Second Tropes.

Featured on EQD.

Cover art by Swirling Line.