Microwave butter and marshmallows in large microwavable bowl on HIGH 1-1/2 to 2 minutes or until marshmallows are puffed. Stir in gelatin until well blended.
Pour marshmallow mixture over popcorn in large bowl; mix well. Shape into 12 balls with lightly greased or moistened hands.
Top each ball with a gumdrop piece to resemble pumpkin stem. Decorate with melted chocolate to resemble jack-o'-lantern faces.