Prepare and bake the chocolate cake according to package directions in a 9x13-inch baking dish.
Cool cake for 10 minutes. Use the handle of a spoon to poke holes evenly across the cake. Microwave hot fudge until pourable and spread evenly over the cake, allowing it to seep into the holes. Cool completely.
Whisk one box of pudding mix with milk. Before fully set, spread evenly over the cooled cake. Refrigerate for 20 minutes.
Whisk remaining pudding mix with milk and refrigerate 10 minutes until set. Fold in Cool Whip, then mix in three-quarters of the crushed Oreos.
Spread topping evenly over the cake and sprinkle remaining crushed Oreos on top.
Serve immediately or refrigerate until ready to serve. Chill at least 1 hour for cleaner slices.