In a large mixing bowl, whisk together the instant vanilla pudding mix and 2 cups of cold milk. Continue whisking for about 2 minutes until the mixture starts to thicken and becomes smooth.

Gently fold in the 8 ounces of thawed whipped topping into the pudding until fully combined using a spatula.

Add the coarsely crushed Oreo cookies and optional mini marshmallows to the mixture. Stir until evenly distributed.

Transfer the mixture into a serving bowl or individual cups, cover with plastic wrap, and chill in the refrigerator for at least 1 hour.

Once chilled, serve your Easy Oreo Fluff with additional crushed Oreos or a dollop of whipped cream for garnish.