Cut several ghost patterns, approximately 4 1/2 inches, from brown paper or parchment. (A round 3 1/2-inch cutter may be used to create desired shapes.)
Cream butter in a large mixing bowl; gradually add sugar, beating until light and fluffy. Add egg, mixing well. Stir in chocolate and vanilla. Combine flour, soda, and salt; add to creamed mixture, stirring well. Chill 1 hour.
Roll to 1/4-inch thickness on a lightly floured surface; cut into ghost shapes using the precut paper pattern or a round cutter. Remove paper, and place on greased cookie sheets; bake at 350° for 10 to 12 minutes. Cool slightly on cookie sheets; remove to wire racks to cool completely.
Prepare Decorator Frosting. Tint one-third of frosting to desired color. Pipe frosting around outer edge of each cookie, and form eyes, as desired.
Add water to remaining white frosting to create a more fluid consistency. Pipe to cover unfrosted area of each cookie. Let the frosting harden.