In a large greased bowl, combine popcorn and cereal. In a large saucepan over low heat, combine marshmallows and butter. Cook and stir until marshmallows are melted and mixture is smooth. Pour over popcorn mixture. Add M&M’s; stir until combined.
When cool enough to handle, shape 1/3 cupfuls into balls with lightly buttered hands. Place on waxed paper-lined baking sheets. Cool.