Preheat your oven to 350 degrees fahrenheit, and spray a 9x13 inch pan with cooking spray. Set aside.
In a large mixing bowl, whisk together cake mix, oil, water, and eggs. Pour into prepared 9 x 13 inch pan.
Bake according to the package directions, 30-35 minutes.
Lay 9-10 Milano cookies onto a plate, set aside.
Heat your chocolate chips in a microwave safe bowl, in 20-second increments, stirring after each increment. Add melted chocolate to a plastic storage bag, and snip a small tip off of the corner of the bag. Use the melted chocolate to write "RIP" onto your Milano cookies.
Place cookies into the refrigerator to allow chocolate to set.
Add Oreo cookies to a food processor, and pulse until the cookies are crumbs. Set aside.
Scoop the chocolate frosting out of the container and into a microwave-safe bowl and microwave for 20 seconds. Stir frosting and pour evenly on top of cake.
Sprinkle cookie crumbs over the frosting.
Decorate the cake with RIP cookies, candy pumpkins, and gummy worms.