I kept this one small because I started it early October. I have always loved giant spiders and thought it might be fun to have the kids walk through a white, spun-silk tunnel like you see in the grass on a dewy morning and meet up with a huge spider which ... passes out the candy
There were three challenges here. The first was to make the spider big enough to be terrifying, but be able to make it at least somewhat realistic and have it fit into the garage. The second was to make this large creature surprise the kids. The last was to find a mechanism in which the spider can pass out the candy.
My solution to the first issue was to have the spider crawling out of a well (in the middle of my garage). This allowed me to bypass the largest part of the spider (being the abdomen) and concentrate on his head and legs (I could even make fewer than eight legs this way). I also thought of having it peering out over a wall from above but the well was actually an easier solution. This is a picture with the lights on. It looks much cooler under black light.
The second piece, on how to make this large, stationary thing surprise the kids, was not as inventive... I put it behind a curtain. The kids would walk up to a gatekeeper who would say (via recording) "Welcome! Now that you are here, who gets tricked and who gets the treat? Ha! Ha! Ha!" The lights go out and the black curtain rolls up to reveal the black-light lit spider.
The passing out of the candy thing was not too hard to figure out. I attached a small basket to one of the spider's legs and operated the leg like a giant marionette puppet. Worked pretty good as long as the kids didn't get grabby. One warning, I would not do this if the kids in your neighborhood are unruly or they will break your spider (I live in a fairly well-behaved neighborhood and I had to repair mine a couple of times before the night was over).
How to Make a Giant, Candy-dispensing Spider