Twilight has been diagnosed with multiple-personality-disorder, but they do not realize how deep it goes.In the day-time, she is normal but when she's out at night Twilight becomes an entirely different pony, and that is what everyone worries about. The pony she becomes calls herself Nightfall, a wicked dark hearted and furred pony, but not only does her looks and thoughts change, so do her memories. As Nightfall she had no memory of her great friends or family, only knowing that soon she will rule all of Equestria. Will the rest of the mane 6 find a way to cure her? Or do they even KNOW about what Twilight has?

Name goes to DragonLover553 because they came up with the name for evil Twilight.