Preparation

• Line 13x9-inch pan with foil, with ends of foil extending over sides. Spray with cooking spray.
• Prepare brownie batter as directed on package, stirring 2/3 of the chopped cookies into batter before pouring into prepared pan. Top with remaining chopped cookies and Halloween sprinkles.
• Bake 25 to 28 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Cool completely.
• Cut brownie into 30 pieces. Spread a dab of frosting onto one flat end of each marshmallow; place, frosting sides down, on tops of brownies.
• Microwave 1/2 of the remaining frosting on HIGH 10 to 20 sec. or just until warmed and smooth when stirred. (Do not over heat.) Spoon evenly over tops of marshmallows on 15 of the brownies, letting frosting run down sides of marshmallows and onto tops of brownies.  Add black disc-shaped sprinkles to coated marshmallows for the ghosts' eyes.
• Microwave remaining frosting, then spoon over remaining marshmallow-topped brownies as directed. 
• Let brownies stand 10 min. or until frosting is firm.