Bake cupcakes according to the package directions and cool completely before frosting.

Add candy melts in a microwave safe bowl and microwave for 60 seconds at 50% power. Stir and return to the microwave. Heat in 30 second increments at 50% power and stirring until melted. Add cornstarch and mix well. A dough like clay will begin to form. Mix until evenly combined.

Place candy clay onto a piece of plastic wrap and flatten. Wrap with plastic wrap and set aside to cool.

Knead candy clay until soft and smooth. Use a rolling pin dusted with cornstarch to roll the clay ⅛" thick. use a round cutter to create moon like shapes, and cut the moon i half to make a shark fin. Repeat until you have 24 shark fins made.

Fit a piping bag with a 1M decorating tip. Spread ½ cup of white frosting along one side of the bag. Tint the remaining frosting with blue food coloring. Frost each cupcake with a thin layer of blue frosting. Place remaining blue frosting into the piping bag.

Press one shark fin into each cupcake in the center. Pipe icing around the fin to look like water. Repeat until all 24 cupcakes are frosted.