Heat oven to 350°F. In large bowl, combine cake mix and margarine; mix well. Stir in egg; blend well. Press mixture in bottom of ungreased 15x10x1-inch baking pan.
Bake at 350°F. for 10 to 14 minutes or until set and light golden brown around edges.
Remove pan from oven; immediately sprinkle with marshmallows. Return to oven; bake an additional 1 to 2 minutes or until marshmallows just begin to puff. Cool while preparing topping.
In large saucepan, combine corn syrup, sugar and brown sugar; blend well. Cook over medium heat, stirring constantly, until mixture comes to a boil.
Remove from heat; stir in peanut butter and vanilla until well blended. Stir in cereal, peanuts and candy corn. Immediately spoon warm topping over marshmallows; spread to cover. Refrigerate 30 minutes or until firm. Cut into bars.