Place popped popcorn into a large bowl.

Combine corn syrup, butter, water, confectioners' sugar, and marshmallows in a saucepan over medium heat. Heat and stir until the marshmallows have melted and the mixture comes to a boil.

Carefully pour hot marshmallow mixture over popcorn and toss together to coat each kernel evenly.

Grease hands with cooking spray and quickly shape coated popcorn into balls before it cools too much to shape.

Wrap balls with cellophane or plastic wrap and store at room temperature.