Melt semisweet chocolate according to the package instructions. Holding the open end of the cone, dip the bottom half at an angle into the melted chocolate. Immediately press candy pumpkins into the chocolate. Place the cone on waxed paper and let sit until the chocolate sets.
Frost the top and side surfaces of a doughnut with icing. Sprinkle icing with nonpareils or sprinkles. Center the open end of the cone on the frosted doughnut. Use a sharp knife to cut candies or gum pieces into quarters and adhere them around the bottom of the hat with icing.