The mother of all Halloween parties, the annual Music Box Massacre is a 24-hour marathon of classic horror movies, vintage trailers, and personal appearances, with a collectibles market in the theater lobby. Among this year’s guests are the Chiodo Brothers, the special effects artists behind Killer Klowns From Outer Space (1988), and Jan White, who appeared in George Romero’s Season of the Witch. Tickets are $28 in advance at brownpapertickets.com (last year’s event sold out) or $33 at the door, and patrons may leave and reenter the theater. For more information see musicboxtheatre.com.