A Púca is a legendary shapeshifter, said to bring both good and bad fortune. One has not been seen in Equestria in nearly a thousand years. Ponies thought them extinct, dead, deceased. Celestia had even stopped teaching about them, having herself forgotten they could still exist. So naturally, when one shows up in Ponyville, ponies mistake it for a black goat.

Pooka isn't going to let this insult slide. Ponies must be taught a lesson.