Sunset Shimmer finally returns home to Equestria to right her old wrongs, unfortunately the sins of the Human World follow her back and put everypony in Equestria in danger.
A year after the battle of the bands, graduation nears, a familiar face returns, a pure heart is corrupted, enemies become allies and the fate of all reality hangs in the balance.
Mario and co. are ready for a relaxing vacation with Peach's royal friends in Equestria. Little do they know that something so innocent will inevitable lead to their next big adventure.