Begin by crushing the Oreo cookies in a food processor until they're fine crumbs. Reserve half a cup of the crumbs for topping later. Press the rest firmly into the bottom of a 9x13-inch dish, creating an even crust. Set it aside.

In a large mixing bowl, combine the softened cream cheese, unsalted butter, and powdered sugar. Using an electric mixer, beat on medium speed for about 2-3 minutes until the mixture is smooth and creamy. Gently fold in the thawed whipped topping.

In another bowl, whisk together the instant vanilla pudding mix and cold milk for about 2 minutes until thickened. Let it sit for 5 minutes to set. Fold this pudding mixture into the cream cheese mixture.

Spread the creamy filling evenly over the prepared crust. Sprinkle the reserved Oreo crumbs, mini Oreos, and pastel candy-coated chocolates on top.

Cover the casserole and refrigerate for at least 2 hours. For the best results, let it chill overnight before serving.