Preheat the oven to 350°F.
In a medium mixing bowl, add the softened cream cheese, sour cream, ranch seasoning mix, buffalo sauce, and garlic powder. Mix together until smooth and fully combined. Add the shredded rotisserie chicken and cheeses to the bowl and stir with a spatula until the chicken is evenly coated with the mixture.
Transfer the mixture to an medium baking dish and spread it evenly with a spatula.
Bake for 20 to 25 minutes, or until the dip is hot and bubbly around the edges.
Remove from the oven and let cool for 5 minutes. If desired, sprinkle the top with thinly sliced green onions and blue cheese crumbles for garnish.
Serve warm with tortilla chips, celery sticks, or carrot sticks.