While exploring Canterlot Castle, Pinkie and Rainbow Dash uncover a room filled with stone tablets connected to dials. Above each dial is the name of an alicorn. These couldn't possibly control an alicorn's power, could they?
Conversion Bureau storyline. When Celestia started her plans for Conversion, she could not imagine that a group of teens would have come to stop her, and by stealing what she could not defend: the Hearts of Equestria. The Phantom Thieves are Back!