Cook brownie mix according to package directions and cool completely. Cut into 1-inch squares. In a large bowl, combine pudding mix, water and sweetened condensed milk. Stir until smooth, then fold in 8 ounces whipped topping until no streaks remain. In a trifle bowl or glass serving dish, place half of the brownies, half of the pudding mixture and half of the 12 ounce container of whipped topping. Repeat layers. Refrigerate 8 hours before serving.
You can shave a chocolate candy bar onto the top to add a pretty garnish.