Divide the 9 cups Chex cereal evenly between two large bowls, with 4 1/2 cups in each bowl.
In a microwave-safe bowl, combine 1/4 cup chocolate chips, 1/4 cup peanut butter, 2 tablespoons butter, and 1/2 teaspoon vanilla extract.
Microwave the mixture for 30 seconds. Stir well, then continue microwaving in 15–30 second intervals, stirring after each interval, until completely melted and smooth. Do not overheat.
Pour the chocolate mixture over one bowl of 4 1/2 cups Chex cereal. Gently fold with a spatula until the cereal is evenly coated.
Place 1 cup powdered sugar in a large gallon-size zip-top bag. Add the chocolate-coated cereal, seal the bag, and gently shake until the cereal is evenly coated with powdered sugar.
Repeat the process with the remaining 1/2 cup white chocolate chips, 1/4 cup peanut butter, 2 tablespoons butter, and 1/2 teaspoon vanilla extract. Microwave in short intervals, stirring between each, until smooth.
Pour the white chocolate mixture over the remaining 4 1/2 cups Chex cereal and gently fold until evenly coated.
Place the remaining 1 cup powdered sugar in a clean gallon-size zip-top bag. Add the white chocolate-coated cereal, seal, and shake gently until evenly coated.
Spread both puppy chow mixtures onto a large baking sheet and allow them to cool completely.
Once cooled, gently combine the two puppy chow mixtures. Add 1 cup candy corn and candy eyes, then gently toss to distribute them evenly.
Serve immediately or store in an airtight container at room temperature.