Preheat oven to 350°F. Spray a 9x13-inch baking dish with nonstick cooking spray.
In a large bowl, mix together the chicken, ranch seasoning, buffalo sauce, cream cheese, ½ cup of mozzarella cheese, and pepper until well combined.
Stuff each jumbo shell with the chicken mixture and place in the prepared baking dish.
Top with the remaining mozzarella and the white cheddar cheese. Bake for 15-20 minutes, or until bubbly.
Drizzle with ranch dressing and buffalo sauce.
