Castle Mane-ia

Castle-Mania is an upcoming episode of My Little Pony Friendship is Magic. It is the third episode of the fourth season, and the sixty-eighth episode overall. The title of the episode is an allusion to Castlevania, the Konami series of video games.

Summary
The episode's credited cast of characters consists of Twilight Sparkle, Spike, Construction Pony, Pinkie Pie, Fluttershy, Rarity, Princess Luna, Apple Jack [sic], Rainbow Dash, and Princess Celestia.

Summary from Hub Network
"Twilight and Spike are sent by Celestia to the ruins of her old castle for research, and unknown to each other, the rest of the ponies find their way there as well. Meanwhile, trap doors, secret passages and a dark presence known only as the Shadow Pony await them"

Summary from Zap2it
"While in Luna and Celestia's old castle, the ponies are convinced it is haunted by the Pony of Shadows."