The princesses gave their magic to Twilight to prevent Tirek from stealing it. As a result, they end up stuck in Tartarus.

Marvelous place, Tartarus. Really brings ponies together. The fact that things manage to go downhill here says a lot about the wonders of family and alicornhood.

Spanish translation by SPANIARD KIWI

Audio Drama by Espa_Roba_5 and Ajvasquezbrony28
Live reading by The Living Library
Live reading by Astro-Brony

Proofread by Octavia Harmony

For almost a thousand years, the immortal Nightmare Moon has reigned over Equestria as Empress. To the average pony, Nightmare Moon is an overarching enigma whose rule is absolute and whose wrath is terrible. But to Twilight Sparkle, who as an orphan has never known her parents, the Empress is something else entirely. When the young unicorn is brought under the royal wing as an apprentice, she learns a great deal more about the supposed tyrant than she ever knew. But as Twilight is introduced to life with her new mentor, she is thrust into a world of political intrigue, conspiracies and secrets. Secrets that were never meant to be revealed. As allies and enemies plot against the very peace of the nation, will Twilight fall prey to the perils of her new position? Or will she prosper and find in Nightmare Moon the mother she never had?

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My eternal gratitude to my editor, LordOfTheWrongs, without whom Night's Favoured Child would not be the story it is today.

Now with added TVtropes!

Twilight Sparkle has too much magic, and it will take her decades to learn to control it. Her spectacular loss of control during her entrance exam only proves that fact. She is a danger to herself and others.

After Sunset Shimmer’s disappearance, Princess Celestia needs a new student to bear The Element of Magic to defeat Nightmare Moon. With all of Equestria at stake, Twilight Sparkle…is not the pony she needs.

Princess Celestia seals Twilight Sparkle’s magic with the distant promise of one day teaching her.

But there are two diarchs of Equestria. Amidst a lucid dream, an offer is made.

“Hello, Twilight. Would you like to be my student?”

Cover art provided by Lafiir.

This story is a sequel to The Celestia Code

When the monsters created by the dark crystal engine escape their prison, it's up to Princess Twilight Sparkle to deal with them. She gets help and advice from Princess Luna, but things don't go as planned. In fact, when a pony who relies on logic and rationality tries to navigate the stormy seas of emotional entanglement while simultaneously saving Equestria from a horde of evil creatures intent on destroying everything they encounter, nothing goes as planned.
AUDIOBOOK by VisualPony
WARNING: Major spoilers in the comments.

Book 2 of the Alicorn Adventure series.

Goodreads Page
100% Approved by Twilight's Library!

The Badass Twilight tag applies more than ever, but please note the new tags.

This story is a fairly direct continuation of The Celestia Code. You might be able to follow it without having read The Celestia Code first, but it's better if you do.

The sequel is here: The Twilight Enigma

Most excellent pre-reading/editing done by the erudite AcademicPony and the dapper statoose!

Twilight Sparkle's tenure in Ponyville has been anything but calm. Since the Summer Sun celebration, she's dealt with a variety of foes, from Nightmare Moon to dragons, hydras, Discord, and King Sombra. But when Pinkie Pie asks for help with a small problem, Twilight finds herself pulling out all the stops to deal with the most dastardly (and curious) fiend yet encountered: Sugarcube Corner’s haunted mailbox. Rainbow Dash’s letter from the Wonderbolt Academy is on the line. Failure is not an option.

One day, Rainbow Dash wakes up to discover she is a fully-fledged alicorn. How will she use her great powers? And more importantly, how will she break the news to Twilight?

Twilight isn't having a very good day. An experimental spell blew up in her face, an army of changelings is attacking Canterlot, and she just died. Yet somehow, it looks like it's going to keep going downhill from here.

Given the chance to correct what's gone wrong, Twilight swears she's going to fix all this even if it kills her. Which it will. Frequently.

Cover art by Pixel Prism
Spanish Translation
Series TV Tropes page

In the wake of Rarity’s ‘improvement’ spree, the Princesses have a discussion about their duties and what it means to be a princess… also they complain a lot… In fact they mostly just complain.

Have you ever woken up as a vegetarian cartoon pony? I have, and she won’t shut up about it. I’m stuck in her body as our minds swap control and our memories blur. I can’t seem to do anything right, and it’s even worse when she’s in charge.

Now, we’re in a back and forth war for control of her body. I just want to eat meat again, and have a little personal space. She’s convinced I’m hitting on her friends and trying to score. I’m not sure I can survive the rest of the day, let alone until we fix this.

Edits by: Selbi, Abcron, Breath of Plagues, Refro, Jaestring, The Parasprite, Starbound Gurren
Pre-read by: SkeeterTL, Solidfire, Penjacker, TypewriterError, Pearple Prose
(It took all of them to corral my insanity.)
Cover art by Tsitra360
V1.1-Rated teen sex for strong innuendo.
V1.2-Pinkie Pie now enforcing RIAA guidelines.

Princess Twilight Sparkle discovers a centuries-old mystery hidden in the Royal Archives. Her investigation leads through layer after layer of deception and misdirection, setting her hooves on a path that seems to be leading to a mysterious secret. Along the way, she learns that some friendships can be very, very strange.

Book 1 of the Alicorn Adventure series.

AUDIOBOOK by VisualPony
Featured at the Royal Canterlot Library
TV Tropes Page (Courtesy of Sandtalon)
Goodreads Page (Courtesy of Facedeer)
Equestria Daily Page

WARNING: Major spoilers in the comments. Takes place several months after the end of season four. (Not a Da Vinci Code crossover, BTW!)

Do you see a dark tag? No, you don't. Not dark. Well, okay, there are a couple of dark-ish bits, but that's all. Not enough to warrant a tag. Speaking of tags, there really ought to be "Badass Twilight" and "Friendshipping" ones.

Sequels and side-stories (and more) can be found here Offprint and AO3, and a hardbound two-volume set of all that can be ordered from The Ministry of Image.

My editor for the first edition of this story was Gogito, and I can't thank him enough for all the hard work he did. My editor for the revised version was PresentPerfect, and he did a terrific job of getting the story into excellent shape.