
Just take a regular old welcome mat, add some witchy stockings filled with stuffing, and black witchy shoes. Then take the legs and duct tape them to the back of the mat, so when you place it in front of the door, it lays flat.
I'd also make sure that you have good lighting on the porch, so your guests (and little trick or treaters) don't trip and fall.
Told ya that would be super easy.....