Prepare the Chicken: If using canned chicken, ensure it's well drained and shredded. If using cooked chicken breast, shred it into bite-sized pieces.

Combine Ingredients in Slow Cooker: In a 3-quart or larger slow cooker, add the shredded chicken, softened cream cheese (cut into cubes for easier melting), buffalo wing sauce, and ranch dressing.

Stir to Combine: Stir all the ingredients together until they are well mixed. It’s okay if the cream cheese isn't fully incorporated yet; it will melt as it heats.

Add Cheeses: Sprinkle in half of the shredded cheddar cheese and half of the shredded mozzarella cheese. Gently stir these in, leaving some for the top.

Cook on Low: Cover the slow cooker and cook on LOW for 1.5 to 2 hours, or until the dip is hot, bubbly, and the cheeses are completely melted and smooth. Stir occasionally during the cooking process to ensure even melting and prevent sticking.

Stir and Serve: Once heated through, stir the dip thoroughly to ensure all ingredients are well combined and the dip is consistently creamy.

Final Cheese Topping (Optional): If desired, sprinkle the remaining cheddar and mozzarella cheese on top during the last 15-30 minutes of cooking, or just before serving, to create a melted, bubbly cheese crust.

Garnish and Serve: Transfer the Crockpot Buffalo Chicken Dip to a serving dish, or serve directly from the slow cooker to keep it warm. Garnish with sliced green onions and blue cheese crumbles, if using. Serve hot with your favorite dippers!