Preheat the oven to 350 degrees and place cupcake liners in a cupcake pan.
If making homemade cake mix: Prepare the cupcake batter. If using boxed cake mix, mix according to the package directions. If making homemade cupcakes, whisk together the dry ingredients in a bowl, combine the wet ingredients in another bowl, then stir them together until a smooth batter forms.
Scoop about ⅓ of the batter into a separate bowl. Add 1–2 small drops of blue gel food coloring and gently stir until the batter turns a soft ocean blue. Add another drop or two of blue gel food coloring to the smaller bowl so it’s slightly darker.
Spoon some light colored batter into the cupcake liners, then add a little of the darker blue batter on top. Use a toothpick or knife to lightly swirl the colors together.
Fill the cupcake liners about two-thirds full with batter and bake for about 22 minutes, or until a toothpick inserted in the center comes out clean. Let the cupcakes cool completely.
Make the frosting by beating the butter until smooth, then gradually mixing in the confectioners’ sugar and cream until light and fluffy. Divide the frosting and tint one portion blue.
Place blue and white into a piping bag with a star tip and pipe upward all along the cupcake then in the center. Insert shark fin into the top middle.