Combine the Oreo crumbs and melted butter. Press the mixture firmly into the bottom and up the sides of a 9-inch pie plate. Chill the crust for 15 minutes.
In a large bowl, beat the softened cream cheese until smooth. Gradually beat in the powdered sugar and vanilla extract until fully combined.
Gently fold in half of the thawed whipped topping into the cream cheese mixture. Spread this mixture evenly over the chilled crust.
In a separate bowl, whisk together the instant chocolate pudding mix and cold milk for 2 minutes until thickened. Pour the pudding mixture over the cream cheese layer.
Sprinkle the mini marshmallows evenly over the pudding layer.
Top the pie with the remaining half of the whipped topping.
Chill the pie for at least 4 hours, or preferably overnight, before slicing and serving.
Notes
For a firmer crust, bake the crumb mixture at 350°F for 10 minutes, then cool completely before filling.
You can substitute regular whipped cream for the frozen topping if you whip it yourself to stiff peaks.
Use dark chocolate pudding for a deeper flavor profile.