Preheat oven at 350. Prepare a 9 x 13 x 2" pan with cooking spray and flour. To prepare crust, combine 2 cups cookie crumbs, 1/4 cup sugar, and margarine in a small mixing bowl. Press firmly into prepared pan. Bake for 10 minutes and then chill. To prepare filling, combine cream cheese, remaining sugar, and 1/2 cup Cool Whip in a mixing bowl. In another mixing bowl, combine boiling water into gelatin until completely dissolved. Mix cold water and ice cubes together to make 1 1/2 cups. Stir ice water into gelatin until thickened. Remove any remaining ice cubes. Spoon gelatin over cream cheese layer. Refrigerate 3 hours or until firm. Spread remaining Cool Whip over gelatin layer. Sprinkle with remaining cookie crumbs. Decorate as a "grave yard" by poking sandwich cookies on end into dessert. Decorate the cookies as tombstones with the decorator icing. Scatter candy and pumpkins around the surface.