For a tall white ghoul, use clean scissors to snip one end each from two large marshmallows. Press the cut ends together.
Roll fondant to about 1/4 inch thick. Cut out a 4-1/2-inch-diameter fondant circle. Shape the fondant over the marshmallow stack.
Add eyes and a mouth with decorating gel.
To color ghouls, tint fondant with a small amount of food coloring. For the striped version, roll small ropes of different colors of the fondant. Press ropes together and roll out with a rolling pin. Finish as directed above.
If desired, use small candies for features, attaching them with decorator frosting.