I just remembered a game we played at a Christmas party. It could be modified for Halloween. You would need a piece of plain paper, a pencil, and a book (or something else firm) for each person playing.
Each party guest held a book on top of his/her head, and there was a piece of paper on top of the book (the book was only to give us something hard to write on). Someone told us to draw certain things. For instance, on one side she had us draw a circle on the right side. Then we had to draw a smaller circle on top of the first circle, and then an even smaller circle on top of the 2nd one. Then she told us that we had just drawn snowmen. We had to add a carrot nose, coal eyes, etc. On the flip side of the paper we had to draw a Christmas tree. Then we had to draw balls on the tree (as many as we wanted). Then we drew a couple gifts under the tree and a candycane hanging from the tree. Then we drew a fireplace and mantle, then a fire in the fireplace. Of course we were not able to look at any of the pictures until we were completely done drawing. Then to score our papers she read the directions again, and you got points based on how well you did. For instance, you got a point for each ball on the Christmas tree, for the carrot being on the top ball of the snowman, the fire being in the fireplace, etc. There were also points for getting it on the correct side of the paper (Some thought they had drawn a certain part on the right but had really done it on the left.).
For Halloween, you could give directions for drawing a pumpkin and then drawing a face on it. They could draw a witch. There are all kinds of possibilities.
It was fun to see how close we were on some things and how funny other things turned out.