We used: a black marker, Styrofoam cups and an oven preheated to 300 degrees.
We colored a scary face on to the cup with the black marker. And placed them in the oven for a few seconds. You may need to form them a little bit when they come out of the oven. Do this quickly, they cool super fast.
The cups that were placed on the tops in the oven turned out like this.
And the cups placed on their bottoms turned out like this.
We hung them up in our door way with fishing line.