1000 years ago she was imprisoned in the moon by Princess Celestia, until finally her prison breaks and she is once again freed, where upon she uses her strong magic to capture princess Celestia and prevent the sun from rising, to make Equestria a land of eternal night.
In an attempt to stop Twilight Sparkle and her friends from reaching the Elements of Harmony, the powerful artifacts that Celestia used to defeat her before, Nightmare Moon uses her magic powers to put a series of dangerous threats in their path to hurt, threaten, or lure them off their quest. At the end of "Friendship is Magic part 2" she is revealed as Princess Luna, Princess Celestia's little sister who is very remorseful of her own actions.
- Nightmare moon is a pun on the word mare, which means female horse.
The darker parts of the moon, visible from earth, are called maria. Singular, mare. (However, the word comes from Latin and is prounced ma-ray.)
Nightmare Moon's first appearence is NOT her introduction, she makes a brief camo appearence in Twilight's hourglass around four minutes and forty seconds in.
- The mist on Nightmare Moon's body is actually her mane and tail.