Pinkie had been kind enough to give Rarity a bit of notice - she knew it would be a Nightmare Night party, at least, and that gave her time to work on costumes, both for herself and for anypony who hadn't quite had the chance to dress up. She'd set up a booth with a variety of hats, capes, costumes, and masks - nothing too spooky, mind you. She herself wore a finely-detailed dress; Spike, in an accompanying costume, wore a tiny black cape and a white mask that only covered half his face. She'd long since given up on attempting to teach him to squeak in tune, but he was adorable, and that was what counted.