Lightly butter a 9x13-inch baking pan. In a medium pot, heat marshmallows, butter and cinnamon over medium-low heat, stirring often, until smooth, 3 to 4 minutes. Transfer to a large bowl with corn flakes and quickly and gently toss to coat (try not to crush too many of the flakes). Transfer to pan, spreading it out evenly and pressing down firmly. Set aside in a cool spot for 30 minutes.

Use a buttered, (3-inch) round cookie cutter to cut out cookies and transfer to a large plate. Break pretzels into pieces and firmly insert a curved piece into the top of each cookie to form a stem. Use chocolate and fruit to decorate cookies like jack-o-lanterns.