Prepare brownies according to package directions or your favorite recipe. Let them cool completely and cut into cubes.
In a large mixing bowl, whisk together pudding mix and cold milk for 2 minutes until thickened. Let sit for 5 minutes.
Fold in half of the whipped topping into the pudding mixture to create a light mousse.
In a large trifle bowl or glass dish, layer half the brownie cubes, followed by half of the pudding mousse mixture, and then half of the remaining whipped topping.
Repeat the layers with the remaining brownies, mousse, and whipped topping.
Sprinkle mini chocolate chips on top and add optional toppings like chocolate syrup or berries if desired.
Chill in the refrigerator for at least 2 hours before serving.