Follow package directions and combine brownie mix with oil, water, and eggs. Bake in a 13" x 9" pan, as directed. Remove from oven and allow to cool for about an hour.
Top brownie layer with the frosting, smoothing out evenly.
For topping, combine the chocolate chips, peanut butter and butter in a small saucepan. Cook and stir over low heat until chocolate chips have completely melted and mixture is well combined. Remove from the heat and quickly stir in crisp rice cereal. Immediately spoon the mixture over the top of the frosting layer and gently spread out evenly. Chill until set.
Allow to sit out for 10 minutes before slicing and serving. Bars are delicious served cold or at room temperature.