Preheat the oven to 350 degrees Fahrenheit. Line a cupcake pan with cupcake liners.
Add the cake mix, water, oil, and egg whites to a large bowl and beat on low until moistened. Continue beating on medium for 2 minutes.
Divide the batter evenly between the cupcake liners and transfer to the oven. Bake for 12-15 minutes or until a toothpick inserted into the center, comes out clean. Allow the cupcakes to cool completely before frosting.
While the cupcakes are cooling melt the candy melts. Use the pastry brush to add melted candy to the feet and tail areas of the bunny butt ice cube mold.
Melt half of the white chocolate, and fill the rest of the bunny butt mold with the white chocolate. Freeze for 30 minutes to set the chocolate. Remove from the mold. This mold only has 10 cavities, so you will need to repeat this process 3 times, or use 3 molds.
Place the coconut in a Ziplock baggie and add 10 drops of green food coloring. Close the bag, and shake until the color is blended and uniform.
Frost the cupcakes with the vanilla frosting.
Place a bunny butt in the center of the top of each cupcake.
Coat the rest of the exposed frosting of the cupcakes in a generous portion of green coconut, tipping the cupcakes to dump off any excess.