Although it's not a scary addition to our Halloween decor, I built a lighted sidewalk (the famous effect from Michael Jackson's "Billie Jean" video) to entertain party guests and treat-or-treaters on their way to our door.
Only the wiring was a little tedious, the rest of the construction was pretty simple, and we've gotten lots of great comments and impromptu dancing.
Keep any additional platform low to ground. I don't want people to feel like they're stepping up onto something.
Span the whole 12-15 length of our sidewalk. It wouldn't look too cool if only a few feet were done.
Outdoor-friendly and fairly immune to moisture (we typically get rain in October).
And most of all it would have to work with fairly light people, but not crumble under foot of heavier ones. I had to figure people might start dancing on this, so it'd have to take a fair bit of abuse.