Color frosting using several drops of green food coloring and a few drops of yellow. Frost cupcakes.
Sprinkle a crescent of chocolate sprinkles onto each cupcake for the hair. Place two M&M's sideways into cupcakes for eyes. Using red gel icing, make a squiggly line for each monster's mouth. Pipe scars and two dots for each nose using chocolate icing. Snip licorice laces into 1-1/2-inch pieces, and use to secure mini marshmallows to each face as "bolts".