Frost the cupcakes with the buttercream frosting.

For each cupcake, use the tip of a toothpick to lightly etch the outline of two large Jack Skellington eyes in the frosting.

Slowly pipe black decorator's icing onto the etched lines and then fill in the inner circles. Use another toothpick to spread and smooth the icing.

Pipe on two short lines for a nose. Next, pipe a long line across the bottom of the cupcake for the mouth. For the finishing spooky touch, randomly top the mouth with a bunch of short icing barbs.