In bowl, combine ancho chile powder, coriander, cumin, ginger, pasilla chile powder, sugar, garlic powder, onion powder, allspice, cinnamon, cloves, fennel, cayenne, 1/2 teaspoon chile de árbol, 2 teaspoons salt, and 2 teaspoons coarsely ground black pepper.
Place chicken on jelly-roll pan. Season with spice mixture. Cover and refrigerate for at least 1 hour or up to 8 hours.
Transfer chicken to 3-quart baking dish. Pour 4 cups buttermilk over chicken, turning to coat. Cover; refrigerate at least 4 hours or up to 24 hours.
In 2-quart saucepan, boil mango nectar on high until reduced to 1/4 cup. Stir in honey, 1/8 teaspoon chile de árbol, and 1/4 teaspoon salt. Let cool.
Remove chicken from refrigerator; let stand 30 minutes. Pour oil into 2-inch-deep 12-inch cast iron skillet (or Dutch oven) to reach 1 inch up side. Heat on medium until oil reaches 350 degrees F on deep-fry thermometer. Preheat oven to 375 degrees F.
Transfer chicken from buttermilk to large cutting board; pat dry with paper towels. Discard buttermilk marinade.
Into 2-quart baking dish, pour remaining 2 cups buttermilk; whisk in 1/4 teaspoon salt and 1/4 teaspoon freshly ground black pepper. In another 2-quart baking dish, place flour. Stir in 1/2 teaspoon salt and 1/4 teaspoon freshly ground black pepper.
Working with breasts and thighs, dip chicken into buttermilk mixture, allowing excess to drip off; then dip into flour mixture to coat, tapping off excess. In batches, carefully place chicken in hot oil, making sure not to crowd the skillet.
Fry breasts and thighs 10 to 12 minutes or until golden brown and cooked through (165 degrees F), turning occasionally. If some pieces turn golden brown before insides have reached 165 degrees F, transfer to rack fitted inside 18- by 12-inch jelly-roll pan and bake for 4 to 8 minutes or until cooked through (165 degrees F). Sprinkle chicken with 1/2 teaspoon salt. Reduce oven temperature to 200 degrees F. Keep chicken warm in pan in oven.
Repeat breading process with wings and drumsticks. In batches, fry 6 to 9 minutes or until golden brown and cooked through, turning occasionally. Transfer cooked pieces to prepared pan in oven. Season with 1/2 teaspoon salt. Serve with mango-honey sauce.
