Preheat oven to temperature directed on brownie package.
Line a 9x13 pan with parchment paper.
Prepare brownies according to box directions.
4 minutes before the brownies are fully cooked, pull brownies from the oven, and add marshmallows on the top.
Return to oven for 4 minutes to soften marshmallows.
Remove from oven and spread marshmallows over the top of brownies. Let cool completely.
In a microwave-safe bowl combine chocolate chips, peanut butter, and butter.
Heat on high for 30 seconds.
Stir and repeat until chocolate is melted and the mixture is smooth.
Add cereal and stir to combine.
Drop spoonfuls of chocolate mixture over the marshmallow layer, spreading as evenly as possible.
Put the brownies in the refrigerator for at least 2 hours to chill.
Lift from pan and cut into squares.