Microwave 1 cup of green meltable candy according to the directions on the package. Skewer a marshmallow and roll it in the melted candy to coat the sides. Put it on a wax-paper-lined baking sheet. Repeat for the other monster heads. When all the marshmallows are coated, refrigerate them on the baking sheet to harden the candy. When the coating has set, apply a bit of frosting to the top of a chilled marshmallow and dip it in the bowl of sprinkles. Remove the marshmallow from the skewer and stick it on a cupcake. Pipe on vanilla frosting eyes and add mini chocolate chips for pupils. Use the black decorators' frosting for the mouth.