Put your Jack O Lantern in the oven and roast him. When his meat is soft, scoop it out and use it in a pumpkin cake recipe, and decorate however you think will work.
Make a chocolate sheet cake. Frost with dark chocolate. Buy a variety of Halloween spooky small decorations, grave markers, skeletons, candy cob webs and go to town. Use your imagination.
How about a disgusting eyeball cake? Use a stainless steel mixing bowl to bake a dome shape. Frost with white, add a colored iris, a black pupil, and red veins.
For a spider cake, bake a cake for the body, frost with black frosting,sprinkle black jimmies (as hair),then use gumdrops as eyes and thick black licorice as legs.
You can try doing a graveyard scene for a spooky Halloween cake. Make little tombstones, ghosts made out of marshmallows and use gray icing for a creepy effect.