Prepare and bake brownie mix according to package directions. Cool on a wire rack. Cut into 1-in. cubes.
In a large bowl, beat cream cheese until fluffy. Gradually add confectioners’ sugar; beat until smooth. Fold in 2 cups whipped topping. Place half of the brownie cubes in a 4-qt. trifle bowl or glass serving dish; layer with half of the cream cheese mixture.
In another bowl, whisk milk and pudding mixes for 2 minutes. Let stand for 2 minutes or until soft-set. Set aside half of the pudding mixture. Stir pecans and 1 cup chopped candy bars into remaining pudding mixture; spread over cream cheese layer. Layer with remaining brownies and cream cheese mixture.
Fold 2 cups whipped topping into the reserved pudding mixture; spread over cream cheese layer. Spread remaining whipped topping over top.
Place chocolate syrup in a heavy-duty resealable plastic bag; cut a small hole in a corner of bag. Pipe eight thin concentric circles 1/2 in. apart on the whipped topping. Beginning with the center circle, gently pull a knife through circles toward the outer edge. Wipe knife clean. Repeat to complete spiderweb pattern. Sprinkle remaining crushed candy bars in center of web. Refrigerate until chilled.