After an irritating encounter with Penny, Sheldon retires to his home-away-from-home, his Batcave, his Fortress of Solitude: his office. But the physicist gets more than he bargained for when a strange interdimensional worm hole appears in the Biology department.

Trapped in an unfamiliar, scientifically impossible world. Sheldon has the perfect opportunity to flex his astonishing social skills, or lack thereof. Completely oblivious that the fate of Equestria rests in his hands, Sheldon embarks on a journey of self discovery and love and tolerance... except he doesn't discover anything, and love and tolerance is a waste of time.

Well, maybe he'll learn the value of friendship along the way. But that isn't likely

This story is a sequel to Project: Sunflower

After the events of Project: Sunflower, Erin Olsen has returned to Ponyville, happy to pursue her studies in magic. After everything that happened the year before, she's looking forward to spending her days studying and having fun with her friends.

Meanwhile, on the newly discovered world of Harmony, humans and ponies work together to study this strange new world. However, their arrival causes something ancient to begin stirring. Something that may end up changing everything.

Erin will need all of her courage, all of her cleverness and, of course, all of her friends to see herself through what happens next.

Cover art by Valkyrie-Girl
Editing provided by:
Brilliant Point, Coandco, Ekevoo, Ludicrous Lycan, Merlos the Mad and Razalon the Lizardman.

Life is good for Lyra and Bonbon but something is missing. Bonbon wants more, she wants a foal and Lyra is faced with how to give the love of her life what she wants.

The story continues with Curse of the Werepony

Isolated from her friends and taken prisoner in the middle of a war, Twilight must deal with the very real dangers of being percieved as an enemy as well as the nightmares of her arrival on 'Earth'. Can she overcome her own fears and the fears of her captors? Will the wayward unicorn's assistance be a boon or a curse to the 'humans?' Most importantly, will she ever find her way home?

"In short, it's a story of friendship and plasma rifles, with the emphasis on the friendship. The characters are well written, the XCOM setting is fleshed out very well, and the story is compelling. If you love XCOM, you'll love the story, but even if you've never heard of it, it's more than worth giving the first 3 chapters a read.

There's excellent action later on, but the real strength lies in the collision between the friendly and naive world of Twilight Sparkle and the desperate world of humans fighting a losing war for survival and willing to do anything to turn the tide."

--Arzoo

(XCOM/FiM crossover)
(Cover art commissioned by a friend and created by the magnificent FoxInShadow!)
(Original cover art by the amazing Carnelian can be viewed here!)
(Gore tag for blood and some violence)
(Many thanks to the studius OminousTen, Arzoo, xXFluttershyForeverXx and finally Setokaiva for giving my rambles a once-over)
(Now with it's own TV Tropes page! Get to tropin' folks!)

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

The Well of Eternity a place lost to time, is the birthplace of Equestria's various deities. King, a mortal man from Earth slips between the cracks that separate worlds. Landing in the unforgiving badlands of greater Equestria, he aimlessly wanders through the unforgiving terrain. Eventually enslaved by diamond dogs, for ten long years he labors under their cruel whips, eventually escaping his captors only to become lost in the depths of Equestria's vast underworld. Dying of thirst, the man spies the Well of Eternity and drinks his fill. Its waters more than quench his thirst; a metamorphosis occurs and changes him, for good or ill none can tell. What fate shall befall this man, the Great Slave King?

Book one of four, book two can be found at The Book of Water: The Marriage of the Slave King

TV Tropes Page: The Great Slave King: Special thanks goes to gentlereader Abstract Indigo

Cover art by PoisonSt.