LINE 9-inch square pan with plastic wrap. Arrange cake slices on bottom and up sides of pan; set aside. Stir boiling water into dry gelatin mixes in large bowl 2 min. until completely dissolved. Add ice cubes; stir with wire whisk until gelatin is slightly thickened. Remove any unmelted ice. Add 1 cup of the whipped topping; stir until well blended. Refrigerate 15 min.
POUR gelatin mixture into cake-lined pan; cover with plastic wrap. Refrigerate 4 hours or until firm.
UNMOLD dessert onto serving plate; remove plastic wrap. Frost dessert with remaining whipped topping. Refrigerate until ready to serve. Decorate with ice cream cones and candies to resemble a castle. Store leftover dessert in refrigerator.