Add each color of candy melts to a separate microwave-safe bowl and microwave on 50% power for 60 seconds. Stir after and return to the microwave and repeat 2 more times, stirring after each time in the microwave. 

Use a third and empty bowl to add one dollop of each color of candy melt to the bowl. Swirl colors together and spoon into the mold, sliding the candy melts up the side until completely coated. Repeat until 3 mold cavities are filled. Freeze for 10 minutes. You will not use all the colored candy melts. Remove spoons from the bowls. 

Remove from freezer and add 1 tablespoon cocoa, marshmallows, and sprinkles to each cavity. 

If necessary, reheat the candy melts, heating for 30 seconds at 50% power and stirring until melted. Add a dollop of each color to the top of the mold and use a toothpick to swirl the colors together.

Top with mermaid tail, and sprinkles. You may need to hold the tail for a minute until the chocolate is set. Because of this, work with one bomb at a time. Return to the freezer for 10 minutes. Remove from mold. 

To enjoy: Place bomb in a mug and pour hot milk over it. Stir well until completely melted. Remove any pieces of candy that don't completely melt before serving.