Episode Title:
Castle Mane-ia.
Episode Description:
Twilight goes to Celestia and Luna's old castle to research the chest from the Tree of Harmony, finding a diary kept by the sisters that explains the workings of the castle. Meanwhile, Applejack and Rainbow Dash challenge each other to stay the night in the castle, which they believe is haunted by the Pony of Shadows, while Rarity takes Fluttershy along to the castle to look for old tapestries to repair. The four inadvertently get into several hijinks of traps and devices triggered by themselves, as well as an unknown pony playing on the castle's organ, thought to be the Pony of Shadows. Twilight finds them all in a state of panic and calms them down, and together they find the organ player to be Pinkie Pie, who had followed her friends to the castle, thinking there would be a party.
