In a large bowl, combine the diced corned beef, drained sauerkraut, softened cream cheese, shredded Swiss cheese, Worcestershire sauce, and black pepper. Mix thoroughly until well incorporated.

Roll the mixture into small, 1-inch diameter balls and place them on a parchment-lined baking sheet. Chill them in the refrigerator for at least 30 minutes, or freeze for 15 minutes, to help them firm up.

Prepare three shallow dishes with flour in the first, beaten egg in the second, and Panko breadcrumbs in the third.

Dredge each chilled Reuben ball in flour, then dip in beaten egg, and finally roll in Panko breadcrumbs until evenly coated. Return coated balls to the parchment-lined baking sheet.

**Frying:** Heat vegetable oil to 350°F (175°C) and fry balls in batches for 3-4 minutes until golden brown, then drain on a wire rack. **Baking:** Preheat oven to 400°F (200°C), lightly spray balls with cooking spray, and bake for 15-20 minutes, flipping halfway, until golden and heated through.

While the Reuben balls are cooking, whisk together mayonnaise, ketchup, sweet pickle relish, Sriracha or hot sauce, Worcestershire sauce, and onion powder in a small bowl until smooth. Adjust spice level to your preference.

Serve the hot Reuben Balls immediately with the spicy Thousand Island dipping sauce on the side.