"You can use any chocolate cake or brownie recipe for this graveyard cake and it is a guaranteed hit for your halloween party or while kids are getting ready to trick or treat. If you like you can add gummy worms as well."
Preheat oven to 350 degrees F (175 degrees C). Grease sides and bottom of a 9x13-inch cake pan with cooking spray.
Combine cake mix, water, eggs, and oil in a large bowl; beat with an electric mixer on low speed until moistened, about 30 seconds. Beat at medium speed until batter is smooth and creamy, about 2 minutes. Pour batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, 26 to 31 minutes. Remove from oven and cool pan on wire rack for 15 minutes. Remove cake from pan and cool completely on wire rack before decorating, about 2 hours.
Spread a layer of chocolate frosting over top of the cake.
Fill a pastry bag, fitted with a small plain tip, with a few tablespoons of chocolate frosting. Write "RIP" or draw a cross on sandwich cookies. Insert decorated cookies into the cake so that they look like tombstones in a graveyard. Sprinkle chocolate cookie crumbs in between the cookie tombstones to resemble dirt.