In the past few months, we have covered plenty of cool DIY robots here. This Robotic Headless Horseman project is another one you may want to try for Halloween next year. DivideWorks used a JD Humanoid robot to pull this off. It is a customizable robot platform with vision tracking, speech recognition, and a whole host of other fun features.
As far as the pumpkin goes, you could always 3D print a hollow pumpkin or follow what the developer suggests. More information is available on Instructables. What do you think? How would you upgrade this robot?