Preheat oven to 180°C (160°C fan forced) Line a 12 hole (1/3 cup) muffin tray with cupcake cases.
Mix the eggs, butter, milk and cake mix in a large bowl with electric mixer on LOW speed for 30 seconds, then on MEIDUM speed for 2 minutes. ( Do not eat batter as it contains eggs)
Divide batter evenly between the 12 cupcake cases.
Bake in the oven 14 to 16 minutes or until tops spring back when lightly touched in centre. Remove from the oven and leave to cool on wire rack. Cool completely.
Divide frosting into 4 small bowls and stir enough food colouring into each to create blue, green, red and yellow frostings.
Spread a heaped tablespoon of the frosting onto each cupcake and smooth down with a spoon. Arrange the sugar candy-coated chocolates in different colours to create scales and mouth, the banana foam for a tail, and the half marshmallow for an eye. Finish off by adding a pupil to each marshmallow with the writing frosting pen.