Dorcas & Sally
Sally had decided to not go to the party through the actual entrance. After all, she had a potion that allowed her to walk through objects! She may as well take advantage of it. Though, as she quickly learned, the empty classrooms that were in between the Hufflepuff common room and the Great Hall tended to be, uh, occupied. Halfway there, she started just running through the rooms with her eyes closed.
Of course, which meant that she made it to the great hall without evening noticing until she noticed that it was much louder. She peeked open her eyes and immediately relaxed, looking around her and noting the shocked expressions of some people. Sally just waved. "You'd be surprised what people do when they don't think someone will walk through a wall, right?"