Study pictures of gargoyles. In Medieval times they placed these grotesque images of evil around churches to ward off evil itself.
Cut out three layers of  cardboard and glue them together, to represent your face of evil. Paint your card white all over and allow to dry completely. Then paint grey into the edges, with a brush that has been rubbed on a piece of old newspaper so that it only has a little paint left in it. When it is dry, do the same with a smaller brush, adding black into the edges.
Draw a picture of evil, to help you design yor gargoyle.