Preheat your oven to 350°F (175°C). Combine the brownie mix, eggs, oil, and water in a large bowl. Fold in chocolate chips if using.
Pour the batter into a 9x13-inch baking dish that has been lightly greased or lined with parchment paper. Bake for 22-25 minutes until just set in the center.
Allow the brownies to cool completely before adding additional layers. For faster results, place the pan in the refrigerator for 30 minutes after it's reached room temperature.
Beat the cream cheese and peanut butter together until smooth. Add the powdered sugar and vanilla, mixing until fully incorporated.
Gently spread the peanut butter mixture over the cooled brownie layer, taking care not to pull up any of the brownie. Use an offset spatula for the smoothest application.
Whisk together the instant pudding mix and cold milk for 2 minutes until it begins to thicken. Pour over the peanut butter layer and spread evenly.
Place in the refrigerator for 15-20 minutes to set before adding the final layer.
Carefully spread the whipped topping over the set pudding layer. Sprinkle with crushed peanut butter cups and drizzle with chocolate syrup just before serving.