Character: nightmare moon
Nightmare Moon is the embodiment of Princess Luna's jealousy over the adoration her sister, Princess Celestia gets, bent solely on bringing forth an Eternal Night. She appears much older and larger than her true self, and is comparable in size to Princess Celestia. Nightmare Moon's body is completely black, her eyes are turquoise and appear more like a dragon's eyes than a normal pony's. Her mane and tail are rather nebulous appearing like the night sky itself, which shows the ability to control them like extra limbs. She was vengeful, condescending, jealous, and angry. The legend that is narrated in the friendship is magic (episode) tells that these negative feelings turned Princess Luna into Nightmare Moon in the first place.
She was thwarted in her plans to cast Equestria into an Eternal Night twice. First, 1000 years before the show takes place, when she was banished to the moon by Princess Celestia, using the Elements of Harmony, and then again during the first episode when she escapes her imprisonment and is stopped by Twilight Sparkle and her friends, each of which embody a respective element. Instead of banishing Nightmare Moon back to the moon, they use it's power to strip the evil away from the mare and turn her back into Princess Luna.
Lauren Faust stated that Princess Luna herself was never evil, but that Nightmare Moon is the result of her becoming possessed or controlled by some evil magic that has yet to be explained.
The following tags are aliased to this tag: nightmare_moon_(mlp)