PREHEAT oven to 350°F. Chop 8 of the cookies; set aside.
PREPARE brownie mix as directed on package; spread batter into greased 14-inch pizza pan. Bake 18 to 20 minutes or until done.
SPRINKLE marshmallows over top of hot brownie; bake an additional 3 to 5 minutes or until marshmallows are lightly browned. Immediately sprinkle chopped cookies over marshmallows. Cool on wire rack.
DECORATE remaining 8 cookies with white decorating icing to resemble tombstones. Stand "tombstones" around pizza, pressing gently into brownie. Decorate with assorted candies.