Preheat oven to 350 degrees and line a 9x13 pan with foil overhanging on each end and spray it with Pam.
Combine cake mix, 1/3 cup of softened butter and egg until combined. Press into the pan and bake for 15 minutes. Remove from oven and immediately sprinkle the top with mini marshmallows and press them into the top of the bars.
Combine corn syrup, 1/4 butter, vanilla, peanut butter and peanut butter chips. Stir over medium heat until the chips are melted. Take off the heat and stir in the cereal and peanuts. Spoon over marshmallows and spread as quickly as possible.
Cool completely before peeling back foil and cutting into bars. You may want to cut them small because they are rich and sweet.