For Halloween this year I pimped out a Jack-O-Lantern with an Arduino! The project consisted of yellow and red LEDs, an Arduino, an ultrasonic sensor, and a breadboard. If you walk up to the Jack-o-Lantern it will transform from glowing yellow to evil red. It was really fun to see the reactions of kids that walked by!
Stealth Mode 
Killer Jack-O-Lantern
To make this project I purchased a plastic Jack-O-Lantern from Jewel-Osco. I did this due to time constraint as well as to prevent the electronics from getting slimy for future use. Being a novice Arduino user this was the perfect challenge to learn more about coding and electronics. I followed this guide on Instructables teaching how to wire and code an ultrasonic sensor to an LED. The easy to follow wiring diagram made it simple to connect all the wires in the right places.
Andrew Stack 