Bake the cupcakes: Preheat the oven to 350°F. Line a muffin tin with cupcake liners, prepare the batter, and fill each liner about two-thirds full. Bake for 16–21 minutes, or until a toothpick comes out clean. Cool completely before filling.
Prepare the filling: Stir strawberry sauce, or warm jam/preserves for 10–15 seconds until thick but pourable. If using red Jell-O, prepare it according to the package and let it cool slightly before adding.
Fill the cupcakes: Poke a small well in each cupcake with a wooden spoon handle, or cut out a small center cone. Add 1–2 teaspoons of filling, then cover the opening if needed. Do not overfill.
Make the blue frosting: Tint white frosting with blue gel food coloring. Spread it over the cupcakes in soft swoops, or pipe short wave-like peaks with a star tip. Chill the frosting briefly if it gets too soft.
Add the sharks: Press one gummy shark into the frosting on each cupcake, or use homemade chocolate shark fins. Add sprinkles, pearl candies, or Swedish fish if desired, but keep the top simple.
Chill or serve: Serve right away, or refrigerate the frosted cupcakes without gummy sharks. Add candy toppers close to serving time, and let chilled cupcakes sit at room temperature for 15–20 minutes before eating.
