I have a plan for Halloween, but I have no clue if I'll be able to do it.
I'll get creepy face makeup, to make my skin look pale or decaying, or something like that. Then, ragged clothes, make my hair go all crazy, and just set a chair down outside my house and watch people. I wouldn't jump out and scare people, just stay totally still, yet make it clear that I am watching them, maybe some eye movements and slowly turning my head as they walk by.
Someone did this behind a bush in a Scream mask the other year, it was scary as hell, so I can imagine this being pretty freaky if done right.