1. Preheat oven to 350°F. Line the cupcake pans with the paper cupcake liners.
2. Prepare the cake mix according to the package directions. Divide the batter evenly between the prepared pans.
3. Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean. Remove from the oven, transfer to a wire rack, and let cool completely.
4. Spoon 1/4 cup of vanilla frosting into a resealable plastic bag; set aside. Tint the remaining frosting green.
5. Spread the cupcakes' tops with the green frosting.
6. On each cupcake, place 2 green M&M'S® close together as eyes. Snip a small corner of the resealable plastic bag, and use the vanilla frosting to pipe dots on the green M&M'S® Brand Chocolate Candies. Attach 2 brown M&M'S® Brand MINIS® Chocolate Candies as pupils. On the back, attach green M&M'S® Brand Chocolate Candies as warts, and then pipe a red mouth with the decorating icing.