Place the chicken in a large resealable plastic bag set in a baking dish. Pour the pickle juice into the bag. Seal the bag and massage gently. Refrigerate 1 to 2 hours.
Meanwhile, whisk the eggs and mustard in a medium bowl; set aside. Pulse the rice cereal in a food processor to make fine crumbs. Heat 1/4 cup vegetable oil in a medium skillet over medium heat. Add the cereal crumbs, panko, 3/4 teaspoon salt and a few grinds of pepper. Cook, stirring frequently, until the crumb mixture is a deep golden brown, 6 to 8 minutes. Transfer to a medium bowl and stir in the garlic powder, celery seeds and dill. Let cool to room temperature.
Place a rimmed baking sheet on the lowest oven rack and preheat to 425 degrees F. Remove the chicken from the pickle juice and pat dry with paper towels. One piece at a time, dip the chicken in the egg mixture, letting any excess drip off, then coat in the crumb mixture, pressing with your hands to adhere.
Remove the hot baking sheet from the oven and brush with the remaining 1/4 cup vegetable oil. Place the chicken on the baking sheet and bake until golden and a thermometer inserted into the breasts registers 160 degrees F and the thighs 170 degrees F, 30 to 35 minutes. Serve with ranch dressing.