1. Combine marshmallows and butter in a Dutch oven. Cook over medium-low heat until melted and smooth, stirring occasionally. Remove from heat.
2. Combine popcorn and graham cracker cookies in a big bowl. Pour marshmallow mixture over popcorn mixture, tossing to coat. Stir in candy corn. Spray hands with cooking spray, and shape popcorn mixture into 3-inch balls, pressing together firmly. Cool on wax paper. Wrap balls in plastic wrap. Store in an airtight container up to 3 days.