Heat oven to 350F degrees. Spray cookie sheet with cooking spray. Mix popcorn and chex in a large bowl and set aside.
Microwave the marshmallow creme in a medium microwaveable bowl uncovered on HIGH for 1 minute; stir. Microwave about 1 minute longer or until melted; stir. Pour over popcorn mixture, stirring until evenly coated. Sprinkle with candies.