There are plenty of themes for Halloween Yard Haunts, but some are so fun that we could see a thousand variations of them and still delight. Here's some fun ones and what folks have done with the themes -
make giant spider will a lawn bag, pool noodles, and black duct tape
For the ones below, I think I'd put a pole in the ground, create an umbrella (painted) and pot underneath painted and upside down. I'd put fiberoptic string lights out of the pot dangling to the ground to cover up the post. Some glow-in-the-dark paint for the pot and umbrella and a blacklight nearby would give it even more impact.
*Don't forget - between old sheets that are tattered and stained with tea to cardboard and some paint, props can be made cheap and easy!