1Heat oven to 350°F (325°F for dark or nonstick pan). Make and bake cake as directed on box for 13x9-inch pan. Cool 10 minutes. Run knife around side of pan to loosen cake; remove from pan to cooling rack. Cool completely, about 1 hour. For easier handling, refrigerate or freeze 30 to 60 minutes or until firm.
2Cut cake as shown in diagram. Tint 1/3 cup of the frosting with 3 drops green food color. Arrange pieces on foil-covered tray to form skate as shown in diagram, trimming pieces to fit. Attach pieces of cake with frosting. Frost with a thin layer of frosting to seal in crumbs. Refrigerate or freeze 30 to 60 minutes to set frosting. Frost entire cake.
3Outline inner throat and tongue of skate with toothpick. Tint 2 tablespoons white frosting with 2 drops yellow food color; frost inner throat. Frost tongue and back of throat with green frosting. Use fruit snack to form brake, strap and back of throat. Make 4 slits in bottom edge of blade, and insert cookies for wheels. Outline skate and blade with decorating gel. Use ring candies for eyelets and wheel axles. Cut 1/4-inch-wide strips of fruit snack and use for laces. Store loosely covered.