After experimenting on her schoolmates' magical music abilities, Sunset Shimmer is haunted by glowy pink butterflies. Surely there's a reasonable explanation for this. Surely.
Everyone has secrets, yet some secrets can hurt others while trying to protect them. Other secrets can also offer salvation, though can be dangerous as well.
Sunset is feeling very lonely this holiday season, so now it's up to Fluttershy and her friends (EQG-verse) to help set things right for the former unicorn.