Begin by crushing all your Oreo cookies until they resemble fine crumbs. Reserve ½ cup for topping later. In a 9x13 inch dish, firmly press the crushed Oreos into an even layer, creating a solid crust.

In a large mixing bowl, beat the softened cream cheese and unsalted butter together until smooth. Gradually add the powdered sugar, mixing until fully incorporated. Fold in the thawed whipped topping.

In a separate bowl, whisk together the instant vanilla pudding mix and cold milk for about 2 minutes, then allow it to rest for 5 minutes. Fold the pudding into the cream cheese mixture.

Spread the creamy filling evenly over the Oreo crust, smoothing it out. Decorate with the reserved cookie crumbs, mini Oreo cookies, and pastel candy-coated chocolates.

Cover the assembled casserole with plastic wrap and place it in the refrigerator. Chill for at least 2 hours for the flavors to meld.