Nightmare Night: The Dark Mare Rises by ShotgunNeko
Link - http://www.fimfiction.net/story/85642/1/nightmare-nightthe-dark-mare-rises/the-dark-mare-rises-and-rises-again-and-yet-again

"When Twilight falls ill, Luna (disguised as Nightmare Moon) cums to the conclusion she needs to get laid.  How many of Twilight's cute little friends can she bed in one night? As many as she wants!  She's THE Nightmare Moon for crying out loud!"

Music used - In the Dark of the Night (1997), Anastasia OST by David Newman
I own nothing in this video.