1.Preheat oven to 180°C. Grease and line three 20cm x 30cm lamington pans. Make cakes according to directions on packets; divide mixture among pans. Bake for 30 minutes. Stand cakes in pans 5 minutes; turn onto wire racks to cool. Using serrated knife, level cakes so they are the same height.
2.Turn cakes cut-side down. Using picture as a guide, make a pattern of the mermaid; cut out tail and body of mermaid from two of the cakes. Cut out fin and two semi-circles for head from remaining cake; discard any leftover cake.
3.To make butter cream; beat butter until white as possible, gradually beat in half the sifted icing sugar then milk, then remaining icing sugar. Beat until smooth.
4.Assemble cakes on prepared board, cut-side down; join with some of the butter cream.
5.Tint two-thirds of the butter cream with green colouring and remaining butter cream with flesh colouring.
6.Spread green butter cream over top and side of tail; spread flesh butter cream over top and side of body and head.
7.Cut spearmint leaves in half length-ways through center; cover tail with slightly overlapping spearmint leaves. Position two green Fruit Sticks to separate tail from body. Position biscuits for arms.
8.Cut mouth from red snake. Position strawberries and creams, upside-down, for eyes; use blue decorating gel to pipe on pupils. Cut two strips of licorice strap for eyelashes; position above eyes.
9.Cut end off pink Musk Stick; position for belly button. Make necklace with Oompas and small shell; position around neck. Position scallop shells and remaining green Fruit Stick, as shown, to make bikini top.
10.Deep-fry vermicelli in hot oil until puffed; drain on absorbent paper; cool. Style and shape hair by cutting and separating noodles; position hair around head.