Mix vanilla pudding and milk together. Place in refrigerator for 15 minutes.
In blender, crush chocolate creme cookies until fine crumbs.
Mix crushed cookies into the pudding mixture.
Fold in entire container of Cool Whip.
Begin with 1 Tbsp chocolate pudding. Mix in. Add small amounts after that to get desired shade.
Refrigerate for 30+ mins. Cut brownies into desired size and shape.
Place "Grey Stuff" into piping bag and decorate brownies in swirls or desired