Twilight becomes alicorn of the stars. This is sort of a problem, because Luna kind of already was alicorn of the stars. Oops!

TV Tropes

After visiting the past in It's About Time, Twilight spends some quality time with Princess Celestia before returning to Ponyville. She then falls into a coma and wakes up where no living pony would ever wish to be, and things only get more complicated when Celestia gets an unexpected visit from herself. Featuring Twilight, Celestia, Luna, The Underworld, and some other alicorn etc.

Celestia leaves to deal with a foreign crisis, giving her sister a chance to rule alone and become more attached to the modern world. She calls on Twilight Sparkle to advise Luna, hoping her student will be able to draw Luna out of her shell. With two major threats to Equestria already defeated in the past year, it seems like the perfect time to let Luna gain some confidence and experience in the modern world. After all, what are the chances of a third disaster occurring?

Now comes with complimentary tropes.

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!

When Princess Cadance and Shining Armor travel to Ponyville for their first anniversary, the Changelings launch an assault on the unprotected city of Canterlot. Taken without warning or without word, the city's defenses fall and Queen Chrysalis claims it for her own, killing Celestia as a token of her victory. With its grand ruler dead, and Princess Luna's whereabouts unknown, something that had been inconceivable in Equestria for over 5000 years now begins to tear it apart--war. (Pre-read and edited by w_o and Lochon)

Because sometimes, a finale isn't the end. Sometimes, pure evil just means you have more to lose.

A changeling's body is the plaything of her mind - but can a changeling ever really change her stripes?

Also because I've wanted to try something approximating an adventure story for a while. If there's any demand for it, I'll continue it properly, otherwise I'll just wrap it up quickly.

After her humiliating defeat at the the royal wedding, the Changeling Queen Chrysalis vows vengeance. After learning from her past mistakes she plans to bring ruin down upon those who wronged her. Is a new dark-age dawning in Equestria?

*Author's notes*

This is my first fic, don't expect high art. While I'm a fairly prolific poet, this is my first foray into prose. Do be gentle.

Queen Chrysalis' cover was perfect. She had removed the two ponies who could interfere, but after they show up at the wedding, can she keep her plans together?

A bit of an alternate ending. It is very similar to the finale, but a different lead up.