Spray a 9x13 in pan with non-stick spray. Set aside.
In a large bowl melt together butter, marshmallows, and peanut butter until smooth. Heat in microwave safe bowl for 30 second intervals, stirring well in between.
3 Tablespoons butter, 10 oz large marshmallows, 1/2 cup creamy peanut butter
Mix in cereal until everything is well coated. Add peanut butter cups and candies and mix to incorporate.
7 cups Reese's Peanut Butter Puffs Cereal
Add peanut butter cups and candies and mix to incorporate.
1 cup peanut butter cups, 1/2 cup Reese's Pieces
Pour into prepared pan, and use a spatula coated in non-stick spray to press down evenly.