Spray a non-stick 13x9 inch baking pan with a non-stick cooking spray.
Mix the yellow cake mix, eggs, water and vegetable oil in a large bowl until blended. Pour into a baking pan, put in the oven and bake for 35 minutes, or until the toothpick inserted in the center comes out clean.
Make the glaze: in bowl mix the melted butter, vanilla, milk and powdered sugar until smooth.
Spread the glaze over the top of the cake. Let the cake cool completely before decorating.
To decorate the Halloween cake, first draw the spider web lines by squeezing the tube of black frosting. Then make the spider shapes by squeezing out the black frosting from the tube (as an alternative, you can use the black prunes to make the body of the spider). Make the eyes of the spiders with red and white frosting dots.
Cover the graham crackers with black frosting, write R.I.P on them with red frosting, then insert the crackers into the top of the cake (just press them into the cake so they remain in an upright position).
Cut the ghost shapes out of marshmallows using scissors. Draw the eyes using the red tube frosting. Put the marshmallow ghosts on the cake.
Use the red frosting to draw bloody swirls around the cake (or on the cake tray outside of the cake).