Place the brownie mix in a medium microwave-safe bowl. Microwave on high for 30 seconds, stir, and repeat in 30-second intervals until the mix has been heated a total of about 2 minutes and reaches at least 165°F throughout.
In a separate mixing bowl, beat the softened cream cheese spread with a hand mixer until smooth.
Add the whipped topping to the cream cheese and beat until light and fluffy.
Whisk the instant chocolate pudding mix into the warmed brownie mix until smooth.
Gradually add the brownie-pudding mixture to the cream cheese mixture and beat just until combined.
Add 6 tablespoons of chocolate milk and beat until light and fluffy; if the dip is too thick, add the remaining up to 2 tablespoons one at a time until you reach the desired consistency.
Spoon the dip into a serving bowl and sprinkle with mini chocolate chips or mini M&M's, if using.
Serve with your choice of dippers such as Oreos, graham crackers, pretzels, vanilla wafers, or strawberries.