MIX 2 cups of the cookie crumbs, 1/4 cup of the sugar and the melted margarine with fork in 13×9-inch baking pan until crumbs are well moistened. Press firmly onto bottom of pan to form crust. Refrigerate.
 
BEAT cream cheese and remaining 1/4 cup sugar in medium bowl with wire whisk until smooth. Gently stir in 1/2 of the whipped topping. Spread evenly over crust.
 
STIR boiling water into gelatin in medium bowl 2 minutes or until completely dissolved. Mix cold water and ice cubes to make 1-1/2 cups. Add to gelatin; stir until slightly thickened (consistency of unbeaten egg whites). Remove any remaining ice. Spoon gelatin over cream cheese layer.
 
REFRIGERATE 3 hours or until firm. Spread remaining whipped topping over gelatin just before serving; sprinkle with remaining 1/4 cup cookie crumbs. Decorate sandwich cookies with icings to make "tombstones." Stand tombstones on top of dessert with candies to resemble a graveyard. Cut into squares to serve.