Line a baking sheet with parchment paper. Put the dark chocolate in a heatproof bowl over pan of simmering water, not letting the bowl touch the water. Once the chocolate is melted, allow to cool slightly then pour into a disposable piping bag.
Snip a small hole in the end of the bag then pipe pairs of bat wings onto the lined tray (draw wing outlines onto the parchment paper if you need a guide), joining the pair together with a blob of chocolate. Place a mini roll between each pair of wings for the bat bodies. Transfer to the fridge and let set for 30 minutes.
Use the white and dark writing icing to draw on the bats' eyes and mouths. Carefully lift each bat off the parchment paper with a flat knife and serve.