While performing an inspection of Tartuarus for Princess Celestia with her friends, Twilight is paying homage to one of Equestria's greatest foes: The Lich known as Dead Horse. Upon arriving, they find the Cerberus dead and all the signs that Dead Horse has escaped. Princess Celestia summons her allies; but she finds that even the combined power of Discord, Shining Armor, and all four Princesses cannot defeat Dead Horse. She accepts that, with the Lich using her own ancient magic against her, only the Rainbow Powers can defeat him. As Equestria falls to the undead armies, Twilight springs a trap in a desperate attempt to bring Dead Horse's attack to a close.