Preheat the oven to 375°F (190°C).
In a large bowl, combine the softened cream cheese, ranch dressing, and buffalo sauce. Mix until smooth.
Stir in the shredded chicken and about half of the shredded cheddar, mixing until evenly distributed.
Spread the mixture into a baking dish in an even layer.
Top with the remaining cheddar and the mozzarella, if using.
Bake for 20-25 minutes, until bubbling around the edges and golden in spots on top.
Top with crumbled blue cheese, sliced green onions, and an extra drizzle of buffalo sauce if desired.
Let sit for about 5 minutes, then serve warm with tortilla chips, celery, and carrot sticks.