Grease a 9x13" pan with baking spray and set aside. 

In a large microwave-safe bowl, melt the butter. Then, add the bag of marshmallows and microwave for about 45 seconds. Remove from the microwave and mix until smooth. Add in the peanut butter and stir. Fold in the cereal and mix until well-coated. 

Spread the cereal mixture into the pan evenly. Then, spread the peanut butter chips and chocolate chips on top, patting down so it sticks to the cereal. Cool at room temperature for at least 30 minutes prior to serving.