Bake the cake mix into cupcakes according the box instructions. Allow the cupcakes to cool completely on a wire rack.

Place the white frosting into a piping bag outfitted with a large circle piping tip and coupler. Pipe the frosting in a swirl on top of each cupcake.

Use kitchen shearsto trim the Airheads candy into 2" sections. Bend the sections into a bow shape and place onto the top of each cupcake, securing the ends down into the frosting. Press miniature marshmallows into the frosting along either end of the rainbow candy piece. Finish with the coin and shamrock sprinkles along one end of the rainbow, if desired.