Following the Apple Family Reunion, Applejack finally has some time to reflect on her life and the many lessons she's learned about friendship, family, perseverance, etc. However, perhaps the most important lesson of all takes a little more...
Hades, Lord of Death and God of the Underworld, is bored. Residing in Tartarus gets tiring for a God. So he decides to visit Equestria for a bit. And maybe make new allies so he can take over Olympus.