Late on Nightmare Night, after the rest of Ponyville has gone to bed, Pinkie Pie descends into the dark and silent basement of Carousel Boutique. Didn't anypony tell her it's not safe to venture out alone at night?
Princess Celestia has been keeping a dark secret from her subjects for a very long time. It's not an easy truth to tell, but if anyone can accept her after learning it, it will surely be her most faithful student.