Prepare brownie mix according to package directions. Cool. Cut into one-inch squares.
In a bowl, combine pudding mix, water and canned milk. Mix until smooth, then fold in the 8 oz, container of Cool Whip. Mix until there are no streaks.
In the trifle bowl, put in half the brownies, then half the pudding mixture and half of the 12 oz. container of Cool Whip. Repeat layers. Places separated sections of Hershey Bar on top of last layer of Cool Whip. Refrigerate eight hours before serving.