Preheat the oven to 180°C (160°C for fan-forced oven). Grease and line 2 x 18cm deep round cake pans with baking paper.
Remove the enclosed frosting sachet from the cake mix and reserve for another use. Make up the cake mix using the vegetable oil, water and eggs called for on the pack instructions. Divide equally between the cake pans and level the tops. Bake for 30-35 minutes or until a round bladed knife inserted into the centre of the cakes comes out clean. Leave in the cake pans for 10 minutes. Remove from the pans and place on a cooling rack to cool. Peel off the baking paper. Cool completely; approximately 1 hour.
Halve each cake horizontally so you have 4 equal layers and sandwich the layers together using three-quarters of 1 tub of frosting. Place the cake onto a cake board the same size diameter as the cake. Spread three-quarters of the second tub of frosting over the top and sides of the cake to form a nice smooth layer. Place in the fridge to chill for 30 minutes.
Place the chocolate in a heatproof bowl. Heat the cream in a small pan until just boiling. Remove from the heat and pour over the chocolate. Let the chocolate melt for 2 minutes, then stir until completely smooth.
Place the cake onto a cooling rack over a baking tray. Pour the chocolate ganache over the top of the cake and using a spatula help the ganache spread down the sides of the cake. Neaten with the spatula and leave to set for 30 minutes.
Spoon the remaining vanilla frosting into a piping bag fitted with a 1.5cm round nozzle. Pipe about 20 individual ghosts onto the top of the cake starting in the middle and placing a pair of candy eyes on each as you go. Press 12 edible ‘eyes’ into the sides of the cake for a super spooky Halloween ghost cake!