Make brownies according to package directions. Let cool, then shred/crumble with a fork into bite size pieces.
Whisk pudding and milk until smooth; fold in Cool Whip.
In a separate bowl, with an electric mixer, cream butter and cream cheese until smooth. Beat in powdered sugar, then add pudding mixture and stir gently to combine.
Layer into trifle bowl or any large glass bowl, starting with pudding mixture, then crumbled brownies, then crumbled Oreos, then repeat. Reserve a few brownie pieces for a final top layer of brownies and Oreos.
Recipe by Hidden Ponies at https://hiddenponies.com/2012/12/saturday-sweets-oreo-trifle/