After a miraculous event at the Summer Sun Celebration, curtsy of Twilight, an evil from ancient Equastria, a being named Undern Slate, awakens from 5,000 years of slumber and begins his quest to conquer all of Equastria, with the help of some old foes from the past and his dark relics; the Elements of Disharmony. To stop this dire threat, the Mane 6 journey to ancient areas of Equastria to uncover the only objects that can stop the newly revived evil. Will they succeed or will Undern rule all with an iron fist…. Sorry, tentacle?