Prep. Preheat the oven to 275°F. Then, pour the cereal into a 9x13 baking dish.
Make the syrup. Melt the butter over medium heat in a saucepan. Add the corn syrup, brown sugar, and salt, stirring continuously. Bring the mixture to a boil and let it boil for about 2 minutes without stirring. Remove from heat, add the baking soda, and stir well until combined.
Bake the cereal and syrup. Pour the caramel syrup over the Chex cereal in the baking dish. Gently stir to coat the cereal evenly, being careful not to break the pieces. Bake at 275°F for 45 minutes, stirring every 15 minutes to make sure an even coating.
Cool. Remove from the oven and let the cereal cool completely in the baking dish. The coating will harden and become crunchy as it cools.
Mix. Once cooled, transfer the caramel-coated cereal to a large bowl. Add the candy corn, cream pumpkin candies, mini pretzels, and candy eyes. Toss gently to combine.