Line a 9x13 pan with parchment paper or foil, and spray with non stick spray
Preheat oven, prepare brownies and bake according to package directions.
Allow brownies to cool and remove from pan using edges of foil or parchment
Cut brownies into 15 - 18 individual pieces.
Top each piece with a large marshmallow.
Microwave white chocolate chips and oil, in 30 second increments, stirring after each, until smooth.
Using a spoon, carefully drip white chocolate completely over the tops of each marshmallow, so they are covered completely and it drips on to brownies.
Allow white chocolate to set.
Use black gel to make eyes and a mouth on each "ghost"