Humans.

Truth or myth? Ancient lost civilization or just an old pony's tale?

No pony has ever seen one, and most haven't even heard of them. But Lyra knows that these wonderful creatures are more than just old legends, and she's going to find out... and possibly drive her roommate insane in the process.

Instead of being killed in the cold Antarctic by Dr. Manhattan, Rorschach finds himself rematerialized in a strange new, pony filled world. He finds himself drawn into the lives of the ponies of Ponyville but some ponies fear that this sociopath will bring danger and darkness to an otherwise peaceful existence. Will the mane 6 help Walter Kovac find peace within himself or will he bring them all down with him in his cold views of reality and existence?

As Seen on Equestria Daily!
And our TvTropes page (By Crowrob0t): http://tvtropes.org/pmwiki/pmwiki.php/Fanfic/RorschachInEquestria

My Little Pony: Friendship is Magic and its likeness is owned by Hasbro Studios. Rorschach and Watchmen are owned by DC comics. All rights go to their normal original, intended owners.

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?

============

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!

After the disastrous invasion of Canterlot, an injured changeling wakes up near a small cottage and is quickly discovered by two of the last ponies she ever wanted to see. Now, with the help of her new "friends," she has to remain undetected in a town high on changeling hysteria that would not hesitate to throw her in the Canterlot dungeons should her true nature be revealed.

Simple, right?

Too bad she couldn't have picked a worse form to stay inconspicuous...

Many thanks to ZuTheSkunk for the cover image!