What to wear: A long peasant dress (with some sort of bodice) and a shawl that's thick and lined with matted hair. Find a crazy-long ratty wig, and tie a pair of antlers to your forehead. For extra points: get some nasty teeth and a scalp to walk around with all night.
How to act: You barely speak, but there's something sinister and unsettling about you. Whisper in the ears of others and ask for them to surrender their souls.