My Little Pony: Equestria Girls - Forgotten Friendship 3a19
Overview:
The story follows Sunset Shimmer, who (using her powers) finds out that her friends' memories of her have been mysteriously erased, resulting in them getting amnesia. Determined to set things straight, she'll need Princess Twilight's help from Equestria in order to find out the source of what caused her friends' memory loss.