In a mixing bowl, beat the cake mix, water, butter and egg until blended (batter will be thick). Spread into a greased 13x9x2 inch pan. Bake at 350F for 22-25 minutes or until a toothpick inserted near the center comes out clean. Sprinkle with marshmallows. Bake 2 minutes longer. Place on a wire rack while preparing topping.
In a large saucepan, combine the peanut butter chips, corn syrup and butter; cook and stir over medium-low heat until melted and smooth. Remove from the heat; stir in vanilla, cereal and peanuts. Spread over marshmallows. Cool completely. Cut with a sharp knife.
Nutrition Info Per Serving: Calories 258 Total Fat 13 g Cholesterol 17 mg Sodium 204 mg Potassium 127 mg Total Carbohydrate 33 g Dietary Fiber 1 g Sugars 14 g Protein 5 g