Special equipment: a deep-frying thermometer
Combine the cornstarch and flour in one bowl, then beat the eggs and 1/2 cup water in a second bowl. In a third bowl, combine the panko and seasoned breadcrumbs. Bread the shrimp by dipping them first in the flour mix, then the egg wash, then the breadcrumbs.
Heat about 1/2 inch of oil in a nonstick skillet over medium heat to 350 degrees F.
Fry the shrimp in batches until golden and crispy, approximately 2 minutes per side. Drain on a paper towel-lined plate and season with salt and pepper. Serve with Cocktail Sauce.
Stir together the ketchup and horseradish in a bowl. Chill until ready to serve.