MIX Crust Mix and butter in 13x9-inch pan until crumbs are well moistened. Press firmly onto bottom of pan.
BEAT milk and Filling Mix in large bowl with electric mixer on low speed until blended. Beat on high speed 3 minutes. (Filling will be thick.) Gently stir in Crushed Cookies until well blended. Spread filling mixture over crust. Garnish with decorating gels and candies to create "spider web" and "spider."
REFRIGERATE at least 1 hour until set. Cut into 12 squares. Store leftover dessert in refrigerator.