Combine popcorn and pretzels in large roasting pan; set aside.
Combine brown sugar, butter, corn syrup and salt in 2-quart saucepan. Cook over medium heat, stirring occasionally, 18-20 minutes or until mixture comes to a full boil. Continue cooking, stirring occasionally, 3-5 minutes or until small amount of mixture dropped into ice water forms a soft ball or candy thermometer reaches 240 degrees F. Remove from heat; stir in baking soda.
Pour mixture over popcorn and pretzels; sprinkle with peanuts. Stir until all popcorn is coated.
Bake 20 minutes; stir. Continue baking 20 minutes. Stir in chocolate pieces and candy corn. Continue baking 5 minutes. Immediately spread onto waxed paper to cool. Store in tightly covered container.