Heat the oven according to the instructions on the box of brownies.
Add the brownie mix to a bowl with the water, oil and eggs. Stir to combine.
Spread the batter into a well greased 9x13 baking dish, and bake according to the package instructions.
Cool the brownies to room temperature.
Spread the marshmallow fluff over the cooled brownies.
Place the peanut butter and chocolate chips into a bowl that is microwave safe. Heat for 30 second intervals until smooth and well combined.
Fold the Rice Krispies into the mixture.
Spread the Rice Krispie layer over the marshmallow cream.
Chill for at least 2 hours before slicing to serve.