I decided more than four years ago that I was going to have an animated tree in my haunted house, but for a while, I couldn't figure out how I was going to get it to move. I went through three prototypes before I settled on this design. I'm really happy with how it turned out.
The outside is made using a cement form, 1x2 wood pieces, and Great Stuff. There are two car vent motors moving the jaws of the skulls and limbs of the tree. The movement is similar to a FCG (flying crank ghost). Also, there are green LEDs for the tree eyes and red LEDs for the skull eyes. They glow with the use of a 555 timer. The limbs were counterbalanced to ensure the load wouldn't be too much for the motor to handle.
An MP3 player with voices wailing makes this one scary prop for Halloween. Here is a video of the finished tree. Sorry it's a little shaky.