I've been doing a Halloween display for the past 20 years, each year I try to add one or two new props.
The electric chair has a jigsaw to make the dummy move back and forth, one strobe under the chair and one above the dummies head plus sound of a guy screaming all is set of by a motion sensor.
The witches cauldron stirs by itself by the use of a rechargable screwdriver motor and the witches head moves back and forth using a oscillating fan, plus sounds of a cackling witch all set off by a motion sensor.
The coffin was made from several doors.
There are two pop-up props run by compressed air, I used pneumatic door openers to make them pop up, set off by a trigger switch.
Most of the dummies were made by wrapping my kids and a mannequin that are clothed in duct tape then cutting them out re-joining where they were cut with duct tape and then stuffed with grocery bags. Some of the hands were made by casting my hands in latex.
A few props like the gator and the guy holding the head and one of the clowns was made using paper mache and coating with a plastic coat.