Princess Luna must go on a diplomatic mission to the isolated city of Marem, and is tasked with choosing a suitable traveling partner to accompany her on the way. She does not choose the talented and magically-inclined Twilight Sparkle, nor the quick and loyal Rainbow Dash, nor even the strong and talented Applejack. Instead, she surprises everypony by taking Pinkie Pie with her and leaving without a word. Not even Celestia can guess the reasoning behind her sister's choice.

For whatever reason, Princess Luna and Pinkie Pie set off to find and negotiate an agreement with the mysterious community of unicorns located beyond the borders of Equestria. What they find there will impact not only Equestria's stance on foreign policy, but the very lives of the two ponies at the center of it all.

Princess Luna, otherwise known as Princess of the Night, realizes, on one starry night, of her pitiful life. With no friends to turn to, she thinks only of the one pony who ever showed her the tiniest bit of friendship. Not those who feared her, or those who pampered her just because she was a princess. But a true friend, by the name of Twilight Sparkle.

Also, someone actually did a dramatic reading of this fiction. Here it is.
http://www.youtube.com/watch?v=dFBrkDCDWX4

This story is a sequel to Petriculture

It's been several months since Pinkie Pie made a stunning admission about her past that permanently changed her relationship with her friends, particularly Twilight Sparkle, but life seems to have settled back to normal (well, normal by Pinkie Pie's standards, at least). However, when an old nemesis returns and ensnares Twilight in her influence, it's up to Pinkie to make things right.

This is the second story in The Petriculture Cycle. There is a TV Tropes Page for the entire Cycle here.

Cover image by Page Turner; "Princess Twilight" vector by Nianara.

Luna has had enough of Celestia's games, and has found the perfect means of revenge. Using a long-forbidden spell, she transforms her sister into little more than a small filly, all so she could pull the greatest prank ever. Unfortunately, she soon learns that before you fool around with dangerous magic, you really need to read the fine print...

A sequel can be found here.

One fine, sunny day in Ponyville, Twilight Sparkle is arrested by the Royal Guard and is convicted of a crime she did not even know anything about, and is sentanced to death in Canterlot.

FINALLY FINISHED!

"And now my dear student, I must wish you goodbye. Forever"

Some secrets should not be shared, Some risks too great. The consequences would just be too dire.
So after Twilight asks her Mentor an innocent question, with a startling answer, the young Mare realises that some secrets are just too dangerous to be shared.

Twilight Sparkle is worried that Princess Celestia's power is fading because of her defeat at the hooves of Queen Chrysalis. She pays a visit to Cadence about the origins of the alicorns in hopes of finding a way to restore Celestia's power. The story goes much deeper than she ever thought and the knowledge may carry dire consequences.

My Little Pony crossed with Breaking Bad:

Several years in the future, a middle-aged Twilight Sparkle is diagnosed with a terminal disease. Facing hospital bills and having severed all ties with Princess Celestia several years ago, and making a meager living as a magic kindergarten teacher, she realizes that she needs to make more money to be able to support Spike.

She sees her opportunity and teams up with Pinkie Pie to produce and sell the popular new illicit drug "Crystal Spark", but runs into difficulties keeping her activities secret, especially since Applejack and Rainbow Dash are leading the Ponyville unit of Princess Celestia's elite anti-drug task force.

The alicorns have been struck by a fatal illness, and Twilight and her friends must find the cure: a panacea hidden in the deepest reaches of Tartarus. But Tartarus is unnavigable to those who cannot withstand the chaos in its depths, and the spirits of harmony are no exception. To obtain this cure, Twilight and company will need to find ponies who can traverse Tartarus, a task that will take them to the edge of the world and back. Supposedly, these ponies have two things in common: they've all crossed paths with the mane six, and none of them ever learn from their mistakes.

Inspired by, but not quite based on, Braid.

AU tag for deviation from Season 3 canon.

Some things in this world happen by chance. Others do not. Twilight Sparkle is about to learn a disturbing truth that will turn her world upside down.

- Originally written May 2011 for Deviant Art

Reading this story first is strongly recommended:
(Blood is Thicker) http://ciroton.deviantart.com/gallery/26378692#/d3e1ndq

Credits:
~Image by JohnJoseco~ ~Edited by BrotherPrickle on Deviant Art~