In large microwavable bowl, microwave butter uncovered on High 30 to 60 seconds or until melted. Add marshmallows; toss to coat. Microwave on High 1 minute 30 seconds to 2 minutes, stirring every 30 seconds, until marshmallows are completely melted and mixture is well blended. Stir in cereal and candies until well coated. Press evenly into pan.