Preheat the oven to 180C (160° for fan assisted ovens) / Gas Mark 4.
Mix the eggs, oil, water and Devil’s Food Cake Mix gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy.
Pour into a large rectangle baking tray.
Bake in the centre of the oven for 23-28 minutes, or until a skewer inserted into the centre of the cake comes out clean, then cool on a wire rack.
Remove 2 tablespoons of vanilla icing and reserve to create the monster’s eyes.
Spoon three quarters of the vanilla icing into a bowl and add in a few drops of the green food colouring. Apply the green icing to the cake covering it entirely.
Add the black food colouring to the remaining icing in the tub and place into a piping bag. Using the picture as a template, carefully pipe the black icing to create the monster’s hair. Then create some eyebrows using the liquorice.
Place the 2 reserved tablespoons of vanilla icing to form the eyes and use the black gel pen icing to outline the remaining facial features.