I'm so big about Halloween that I actually take over one of the physics labs at my school for three days with The Haunted Physics Lab.
Me and the other two physics teachers take turns - each gets one day - to have all of our classes cycle through the lab, where they explore a variety of creepy & weird demonstrations that go through some of the more esoteric physics concepts we'll be covering in the course of the year. The students are encouraged to play around with the equipment, take notes, ask/answer questions, solve puzzles, and generally play while exploring different areas of physics. I also take the opportunity to put together some demos debunking various woo, such as Ouija boards, pareidolia, and (new this year) "ghost detectors".
The Haunted Lab is a huge hit every year, hundreds of physics students go through it an many more non-physics kids drop by during free periods, lunch,
or with other teachers who want to give their kids a little treat. It's not uncommon for some staff members, including the senior administration (principle and even superintendent) to come by for a visit.
The downside: it is a HUGE pain in the ass to set up and maintain. It's not uncommon for me to easily put in about 8 hours worth of work in setting it all up, even though the vast majority of the material & equipment is already in

my room somewhere. So, to make my life a bit more sane, the day before I take my class to the Lab, I show them Randi's "Secrets of the Psychics" video (with a notesheet) so that I can gather equipment, quietly check things in the back of the room, and generally get prepped. I don't usually like to show hour-long videos in class, but that one is a must see, and what better time of the year to do it?
I LOVE Halloween