Steps:

• Preheat oven to 350°. Line bottoms of 3 greased and floured 9-in. round baking pans with parchment; grease paper. In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs, 1 at a time, beating well after each addition. Combine flour, baking powder, salt and baking soda; add to the creamed mixture alternately with sour cream, beating well after each addition. , Transfer to prepared pans. Bake until edges begin to brown, 25-30 minutes. Cool for 10 minutes before removing from pans to wire racks to cool completely., In a microwave, melt baking chips with cream until smooth, stirring every 30 seconds. Stir in vanilla. Set aside to cool slightly. Meanwhile, in heatproof bowl of stand mixer, whisk egg whites, sugar, cream of tartar and salt until blended. Place over simmering water in a large saucepan over medium heat. Whisking constantly, heat mixture until a thermometer reads 160°, 8-10 minutes., Remove from heat. With whisk attachment of stand mixer, beat mixture on high speed until cooled to 90°, about 7 minutes. Gradually beat in butter, a few tablespoons at a time, on medium speed until smooth. Beat in cooled baking chip mixture until blended. , Set aside 1/4 cup frosting. Tint remaining frosting desired shades of blue; spread blue frosting between layers and over top and sides of cake. Tint 1/2 ounce fondant red. Divide remaining fondant in half. Tint 1 portion blue. Leave other half white. On a work surface dusted with confectioners' sugar, roll out blue fondant to 1/8-in. thickness. Using a 3-in. round cutter, cut out 1 circle; repeat with white fondant. Using a sharp knife, cut mouth opening, teeth and body shape on lower portion of white circle. Place white fondant cutout onto blue circle. Roll red fondant to 1/8-in. thickness; cut a small triangle and place in mouth opening, under white fondant and on top of blue fondant. If needed, brush fondant lightly with water to help layers adhere. With remaining rolled blue fondant, cut a crescent moon shape for tail and a triangle for fin. Secure fin and tail to shark body, brushing edges lightly with water, if needed, to help pieces adhere. Secure candy eyes to shark body with small amount of reserved frosting. Place fondant shark on side of cake by pressing gently into frosting. Tint remaining reserved frosting green. Using a leaf tip, pipe seaweed on sides of cake. If desired, decorate cake with sea creature candies and graham cracker crumbs for sand. Refrigerate until serving. Remove from refrigerator 30 minutes before serving. Refrigerate leftovers.