Begin by crushing the Oreo cookies into fine crumbs using a food processor or a rolling pin until they resemble coarse sand. Reserve ½ cup of the crumbs for topping later. In a 9x13 inch dish, evenly press the remaining crumbs down to form a solid crust, ensuring it’s compact and flat. Set the dish aside as you move to the filling.

In a large mixing bowl, beat the softened cream cheese, unsalted butter, and powdered sugar together until the mixture is smooth and creamy, which should take about 2-3 minutes. Gradually fold in the thawed whipped topping until the filling becomes fluffy and light.

In a separate bowl, whisk together the instant vanilla pudding mix and cold milk until the mixture thickens, which should take approximately 2 minutes. Allow the pudding to rest for 5 minutes to firm up, then gently fold it into the cream cheese mixture, combining until well incorporated.

Spread the creamy filling evenly over the prepared Oreo crust using a spatula. Make sure to reach the edges for even distribution. Once the filling is smooth and even, sprinkle the reserved Oreo crumbs on top for added crunch, then add the mini Oreo cookies and pastel candy-coated chocolates.

Cover the casserole tightly with plastic wrap or aluminum foil and refrigerate for at least 2 hours. This allows the layers to set properly, making the dessert easier to slice.