three 8-inch round cake pans; two 6-inch round cake pans; a 3 1/2-inch round cookie cutter; 6 large disposable piping bags; an 8-inch or larger cardboard cake round; a 12-inch square cake drum; a nonstick donut pan; an offset spatula
For the red velvet cake layers: Preheat the oven to 350 degrees F. Grease three 8-inch round cake pans and two 6-inch round cake pans with flour-based baking spray.
In the bowl of an electric mixer, combine the butter and granulated sugar and mix on medium speed until fluffy. Add the eggs and vanilla. Mix well.
In a small bowl, combine the liquid food coloring and cocoa powder. Stir until smooth. Add the mixture to the creamed butter mixture.
Sift together the flour, baking powder and salt. Add the flour mixture to the butter mixture in three additions, alternating with the buttermilk. Begin and end with the flour. Scrape down the bowl and mix again on low speed until no pockets of flour remain.
Combine the baking soda and vinegar in a small cup; the mixture will bubble and fizz. Pour into the cake batter and mix on medium-low speed until well incorporated.
Divide the batter among the prepared pans and bake for 25 to 30 minutes, or until the cakes spring back when pressed in the center. Let the cakes cool slightly in the pans. Turn the cakes out onto a wire cooling rack to cool completely.
When the cakes are cool, use a 3 1/2-inch round cookie cutter to cut the centers from two of the 8-inch cake layers, or use a knife.
Cut a large triangle from the center of each 6-inch cake layer; cut the triangles in half and set aside. Save all of the scraps from the 6-inch cakes for later use.
For the buttercream frosting: In an electric mixer fitted with the whisk attachment, mix together the butter and confectioners' sugar on low speed. Add the vanilla extract and increase the speed to medium. Gradually add milk or cream a little at a time until the mixture thins to spreading consistency. Whip at high speed until the frosting is light and fluffy.
Remove half of the frosting and transfer to a large disposable piping bag with a 1/2-inch hole snipped in the end.
Remove half of the remaining frosting to a separate large bowl and tint with the black, sky blue and royal blue food coloring. Mix in the food coloring 1/4 teaspoon at a time until the desired intensity of blue-grey hue is achieved. Transfer to a large piping bag with a 1/2-inch hole snipped in the end.
Divide the remaining frosting into three separate small bowls; tint one bowl with red food coloring, one bowl with sky blue food coloring and the last bowl with black. Add the coloring 1/4 teaspoon at a time until the desired intensity is achieved. Transfer the red buttercream to a disposable piping bag with a 1/2-inch hole snipped in the end. Transfer the sky blue buttercream to a disposable piping bag with a 1/2-inch hole snipped in the end. Transfer the black buttercream to a disposable piping bag with a 1/8-inch hole snipped in the end.
For the decors and assembly: Place a cake layer with the center removed on a cardboard cake round (8 inches or larger). Pipe a fat line of white (untinted) frosting on top of the cake around the opening. Place the second cake layer with the center removed on top of the first.
Combine the blue sprinkles and fish-shaped candy in a bowl or a jar; mix together. Pour the candy into the center of the cake, filling the empty hole to the top. Pipe a fat line of white icing around the filled hole in the center of the cake. Place the last, whole cake layer on top. Chill the cake in the refrigerator until the buttercream is set, about 20 minutes.
Remove the chilled cake from the refrigerator and carefully cut away two sides of the cake so that the cake is an oval shape.
Place a fat line of white frosting on one long side of the cake; stack the four cake triangles (cut from the 6-inch cakes) upright onto the line of frosting. Frost the entire cake with a thin layer of frosting (crumb-coat). Refrigerate for 20 minutes, or until the frosting is firm.
Frost the cake with additional white frosting. Using an offset spatula, smooth and round the pointed triangle pieces with extra frosting so that it resembles a shark's snout. Refrigerate the cake for 20 minutes.
Pipe a fat line of white frosting around the mouth of the shark and down the front of the cake. Smooth using an offset spatula. Pipe a thick covering of blue-grey frosting on the back of the cake and smooth with a spatula.
Pipe red frosting in the front mouth opening and use the back of a spoon to smooth it into the cavity. You will have leftover frosting; reserve for later use. Refrigerate the cake until well-chilled, about 20 minutes.
Transfer the cake on the cake board to a large 12-inch square cake drum. Pipe a line of blue-grey frosting around the right and left sides of the cake at the base. Use two of the 6-inch cake scraps with rounded edges to create the shark's flippers. Cover the pieces with blue-grey frosting and smooth with an offset spatula.
Use one or two more of the rounded cake scraps to create a fin on the back center of the shark. Cover with blue-grey frosting.
Make a divot on each side of the shark head with the back of a spoon; fill each divot with black frosting. While the frosting is still wet, add a single white confetti sprinkle to each eye.
Remove 35 white candy melting wafers and cut each to a point so they are shark tooth-shaped, using kitchen-dedicated scissors. Insert the teeth into the top and bottom edge of the mouth opening, creating a double row of teeth.
Pipe the sky blue buttercream around the bottom edge of the cake to create water around the shark. Pipe a small amount of leftover white frosting and blend into the blue portion.
Place the remaining candy melting wafers in a microwave-safe bowl and heat in the microwave in 30-second intervals until the candy can be stirred smooth. Transfer the melted candy to a disposable piping bag and snip a small hole in the end. Pipe the candy into a nonstick donut pan. Chill until set, about 20 minutes.
Turn out the candy and place around the bottom of the shark cake in the blue frosting. Pipe four lines of leftover red buttercream to create the appearance of a life preserver.
Allow the cake to come to room temperature before serving. Use a large serrated knife to open the shark's belly in front of an audience. Remove the slice to reveal a cascade of candy fish and ocean blue sprinkles.