Preheat the oven to 325 degrees and lightly grease a skull-shaped cake pan.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt until evenly combined.
In a large bowl, beat the softened butter and sugar until light and fluffy. Add the eggs one at a time, mixing well after each addition.
Stir the vanilla extract and red food coloring into the buttermilk.
Alternate adding the dry mixture and the buttermilk mixture to the butter mixture, beginning and ending with the dry ingredients. Mix just until smooth.
Pour the batter into the prepared skull-shaped pan and smooth the top.
Bake for 50 to 60 minutes, or until a toothpick inserted in the center comes out clean. Cool in the pan for 15 minutes before turning out onto a wire rack.