In a large bowl, combine cake mix, butter and eggs. It will be crumbly. Press mixture in bottom of an ungreased 9 x 13in pan. Bake at 350 degrees for 12-15 minutes. Remove from oven. Sprinkle marshmallows on top and return to oven for 2 minutes.
In a saucepan, heat syrup, butter, vanilla and peanut butter chips. Mix until smooth. Add cereal and nuts. Cover the marshmallow with mixture and chill.