Preheat oven to 350 degrees F.
Liberally grease a 13x9 inch pan with cooking spray.
Set to the side
Prepare the cake according to package directions.
Pour the batter into the baking pan.
Bake as directed on the back of package.
Cool the cake completely.
Once the cake has cooled, poke a bunch of holes.
Heat the peanut butter in a microwave safe bowl, until melted.
Carefully pour the peanut butter over the holes.
Carefully now pour the hot fudge sauce over the holes.
Spread the Cool Whip on top of the cake.
Chop up the candy bar into small bits.
Top the cake with the chopped, assorted candies.
Refrigerate the cake for overnight.