The multiverse theory claimed that all beings must be in their rightful worlds. Otherwise, corruption was sure to pass. With Trollestia, now caged by her counterpart, Molestia, the three mares, plus Trixie must split up, surf the multiverse and set things right.
Trollestia pranks Princess Celestia and Princess Molestia by switching them with their respective universes.
The three mares return to multiverse surfing and hoping to set things right.