Preheat oven to 350°F. Lightly grease baking sheets.
Beat butter and sugar with electric mixer in large bowl until fluffy. Beat in corn syrup, egg and vanilla. Gradually beat in flour, baking soda and salt until combined.
Stir in chocolate chips.
Drop dough by heaping tablespoons onto lightly greased baking sheets. Bake for 9 to 11 minutes or until lightly browned. Cool for 15 minutes on wire rack.
Meanwhile, divide vanilla frosting into 3 bowls, about 3/4 cup each. Stir 1/4 teaspoon gel food colour into each bowl of frosting to make 3 different colors.
Frost bottoms of 2 cookies using same colour; place about 6 mini marshmallows on frosting of one cookie for teeth. Top with second cookie, frosted side down.
Spread different colour frosting on top of sandwiched cookies, attach gummy eyeballs and miniature marshmallow nose. Alternate between colours and repeat for remaining cookies.