For 1000 years, the Princess of Night has been locked up inside the moon, The only evidence that she even exists is the pony shaped emblem in the moon. On the longest day of the 1000th year, Nightmare Moon is released from her prison, and 1000 years of pent up rage is unleashed upon Equestria. it's up to the mane 6, joined by a pony out for revenge, to stop Nightmare Moon and her quest for destruction