Bake and cool two 2-layer cakes. Ice cakes smooth with white icing. Prepare for stacked construction and fondant covering. Tint 72 oz. fondant light blue; cover and stack cakes. Position on foil-wrapped cake board.
Divide 16 oz. fondant and tint fondant as follows: 4 oz. violet, 4 oz. green, 2 oz. ivory, 3 oz. marbleized light peach with white, 3 oz. marbleized light rose with white. Darken 5 oz. leftover blue fondant.
Mold wave border with dark blue fondant. Attach to the bottom borders of both cakes with damp brush.
Mold violet and green coral. Attach to cake sides with damp brush.
Mold the following: 5 peach stars, 4 pink stars, 5 white sand dollars, 6 peach scallops, 6 pink scallops, 3 peach snails, 3 pink snails, 3 peach Auger shells, 3 pink Auger shells. Brush with white Pearl Dust. Attach to sides of cake with damp brush.