Melt the white chocolate, and add a tiny bit of red food colouring, then stir it well to turn it pink.
For the ears and noses for Mouse, spoon 8 oval shapes and 4 smaller circles of the pink chocolate onto baking paper. For the Gruffalo ears, spoon blobs of pink chocolate onto the giant chocolate buttons. Leave to set.
Roll out half of the fondant icing quite thinly. Cut out 4 shapes for the white area of the faces for Mouse, and 20 - 28 small teeth for Gruffalo. Shape 8 horns and 4 or 8 sharp teeth for Gruffalo out of fondant icing.
Take the Mentos / Softmints and, with the black writing icing, draw a small black circle towards the top onto each one to make the eyes for Mouse. Dot each orange Smartie with a little black icing too, to make the eyes for Gruffalo. This can be tricky if the icing is not coming out of the tube very easily (as in my case) - warming it in a cup of hot water for a minute can help a bit.
Cut 24 little strips of licorice to make Mouse whiskers, and a few more to make hair for Gruffalo.
Melt the dark chocolate. Make the buttercream icing by beating together 40g butter and 100 g icing sugar. Add a teaspoon of hot water, beat again, then add another 75 g icing sugar, and more water if needed (may need up to 1 tbsp). Taste and check for consistency, and add more butter / icing sugar / water if needed. Natural icing sugar provides a good colour for Mouse. If you are using white icing sugar, to make it a little darker, add a little of the melted chocolate and beat well, until the buttercream is uniform in colour. Use half to ice four of the cupcakes, then add the melted chocolate to the rest and beat in well, until the buttercream is uniform in colour. Use the dark brown buttercream to ice the other 4 cupcakes.
Use the parts prepared above to make the faces, using a little black writing icing, or licorice strips, for mouths and eyebrows on both. Use a brown Smartie for Gruffalo's nose and a green tic tac or green mini Smartie for his wart. You may find it easier to keep the ears in place by making little cuts into the sponge.
Smile and enjoy!