Heat oven to 350°F. Lightly spray cookie sheet with cooking spray; set aside. Remove 2 biscuits from can; place remainder in refrigerator. To form hat brims, pat or roll each biscuit into 4-inch circle. Cut each circle into 3 equal pieces; set aside.
Cut 1 inch from 2 opposite corners of ham and cheese slices; set aside.
For each witch, pat or roll remaining biscuits into 6-inch circles; spread mustard to within 1 inch of each biscuit edge. Top mustard with 1 slice cheese and 1 slice ham; bring edges of biscuit together in center over ham and cheese, pressing to seal. Place seam side down on cookie sheet.
For hat brim, place 1 piece from a cut biscuit on top of each biscuit sandwich, 1 inch from a pointed end. Sprinkle Parmesan cheese on biscuit below hat brim. Use small knife or toothpick to cut mouth shape into biscuit. Press corn snack into dough to make nose, and top with olive halves for eyes.
Bake 14 to 17 minutes or until puffed and golden brown.