Make candy pieces in advance: Cover patterns with waxed paper. Using melted candy in cut parchment bag, outline and fill in patterns; refrigerate until firm. Carefully remove candy from waxed paper. Pipe accent lines with melted candy on one side of fins and tail; let dry. Turn over and pipe accent lines on other side. Attach lollipop sticks to backs of fins and tail with melted candy. Completely cover sticks with additional melted candy.
Ice two halves of cake together, positioning seam horizontally, and place on foil-covered cake circle. Cover cake with tip 20 stars. Insert candy fins, tail and mouth in cake. Position gumball eyes and pipe tip 3 dot pupils. Mix blue icing with white; do not blend completely. Ice cake circle fluffy, using angled spatula to create waves.