Combine yellow cake mix and softened butter. Beat on low speed until well blended and then add egg. Continue beating until well blended.
Press into the bottom of a lightly greased 9 x 13 inch pan. Bake 12 to 14 minutes or until set and edges are just barely browned. Remove from oven and spread mini marshmallows over the hot layer. Return to the oven for 3 minutes so marshmallows are all puffed up. Remove from oven and cool completely.
After the bars are completely cooled, make the top layer. Combine the corn syrup, sugar and brown sugar in a saucepan. Cook over medium heat, stirring constantly about 2 to 4 minutes or until mixture comes to a boil. Remove from heat and stir in peanut butter and vanilla until smooth. Stir in cereal, peanuts and 3/4 cup of the candy corn.
Drop by spoonfuls all over the marshmallow layer and gently spread around with back of a greased spoon (or fingers sprayed with pam cooking spray) until completely covered.