Preheat oven to 350*. Line 24 muffin cups with paper baking cups. Combine cake mix, root beer, oil, eggs and vanilla in a large bowl. Beat with an electric mixer on low speed until moistened. Beat on medium speed for 3 minutes. Divide batter evenly among prepared muffin cups.
Bake cupcakes until toothpick inserted in centers come out clean, 20-30 minutes. Cool in pan for 3 minutes. Remove cupcakes from pan; place on wire racks to cool completely.
Combine frosting and whipped topping in a small bowl; stir gently to mix. Spread frosting mixture on top of cooled cupcakes.
Sprinkle crushed candy evenly on top of frosted cupcakes.