Add a layer of brownie pieces to the bottom of a trifle bowl. Ensure that the entire bottom is covered. NOTE: to use the entire 2 boxes of brownies, make this layer thick! At least 2 brownies on top of each other.
Next, add a layer of the marshmallow cream (~1-inch thick).
Then add a layer of crushed graham crackers on top of the cream. Repeat these steps a few times, ending on the marshmallow cream layer (also reserving some of the graham crackers and brownie bits for topping).
Top the trifle with leftover graham crackers, brownie bits, mini marshmallows and/or chocolate chips.