Preheat oven to 350 F. Line baking sheets with parchment paper.
In a large bowl cream butter and sugar together. Stir in egg and vanilla.
In a medium bowl, whisk flour and cocoa powder together.
Gradually add dry ingredients to the butter mixture stirring until just combined.
Dust work table with flour. Roll dough out until it is around 1/4 of an inch thick.
Cut out using a gingerbread man cookie cutter.
Bake for 8-10 minutes.
For The Icing: Combine all ingredients until smooth. Pour into a piping bag.
Pipe skeleton design onto cookies. Let sit 1-2 hours or until hard.