Preheat oven to 350 degrees F. Grease bottom of 13x9-inch pan.
Combine brownie mix, eggs, water and oil in large bowl. Stir with spoon until well blended, about 50 strokes. Spread in pan. Bake at 350 degrees F for 27 to 30 minutes or until set.
Spread marshmallow cream gently over hot brownies. Place frosting in microwave-safe bowl. Microwave on high power for 15 to 30 seconds. Stir until smooth. Pour frosting over marshmallow cream. Swirl with knife to marbleize. Cool completely. Cut into bars.
Recipe courtesy of Duncan Hines®