In a large mixing bowl, prepare brownie mix and preheat oven according to directions on package. Coat a 9x13" baking dish with non-stick cooking spray.
Pour half of the brownie batter into the baking dish and spread evenly. Layer with marshmallow fluff, then cover with the other half of the brownie batter.
Bake for about an hour and fifteen minutes, checking often after 45 minutes until a knife inserted in the middle of the cake comes out clean.
For the tombstones
Dip half of an oval-shaped cookie and/or Fun-Sized Butterfinger candy bar in melted white chocolate and allowed to set. You'll want to make 4-8 tombstones.
Once the white chocolate is set, use melted dark chocolate chips and a toothpick to write spooky words like "RIP" or "BOO" on the front of each of your tombstones. Allow to dry.
To decorate your cake
When cake is completely cool, place your candy and cookie tombstones halfway into the cake, spreading them evenly around the cake.
Last, but definitely not least, it's time to place Butterfinger Peanut Butter Skulls on your graveyard cake. We used toothpicks to keep them secure.
Video
Notes
Note: Nutrition information is a rough estimate only; actual values will vary based on the exact ingredients used and amount of recipe prepared.