1Line 13x9-inch pan with foil, leaving foil overhanging at 2 opposite sides of pan; spray foil with cooking spray. In large microwavable bowl, microwave marshmallows and butter uncovered on High 2 minutes. Stir vigorously with wooden spoon until smooth. Add cereal; stir until well coated. Quickly spoon mixture into pan and press evenly. Cool until firm.
2Use foil to lift from pan. Cut with 41/2-inchwide bat-shaped cookie cutter. Press scraps together to use all of mixture.
3In medium microwavable bowl, microwave chocolate chips uncovered on Medium (50%) 2 minutes, stirring once, until softened and chips can be stirred smooth. Spread melted chocolate over bats. Place 2 candy eyes on each bat.