In a mixing bowl, combine the instant vanilla pudding powder and milk. Whisk together until smooth and well combined. Let it sit for about 5 minutes to thicken.
Once the pudding is thick, gently fold in the thawed Cool Whip until fully incorporated. Be careful not to deflate the Cool Whip; you want to keep it light and fluffy.
Next, add the crushed Oreo cookies and mini marshmallows to the mixture. Using a spatula, fold these ingredients in gently until everything is well mixed.
Transfer your Oreo Fluff Dessert Salad into a serving dish and cover it. Chill in the refrigerator for at least 1 hour before serving. This allows the flavors to meld beautifully.
