Cut out a bat symbol on a card and use it as a template.
Use color mist. Lightly place the template over the cupcake and spray the mist over it.
Hold still till the mist settles.
And there you have a ghost like Bat symbol.
Make sure your icing is dry to prevent the template from sticking to your cupcake :)
Mist each cupcake separately and away from the other cupcakes. Mist will travel around to nearby areas.