To make the Coleslaw: Stir together, cilantro, mayonnaise, lime juice, 1/2 teaspoon fajita seasoning. Add 8 ounces shredded coleslaw mix. Stir to coat evenly. Season with salt and pepper to taste. Cover and chill 30 minutes to 24 hours.
To make the Tacos: Peel shrimp; devein if desired.
Whisk together tempura batter mix, beer, and fajita seasoning in a large bowl; let stand 5 minutes.
Pour oil to a depth of 2 inches into a Dutch oven; heat to 325 degrees. Dip shrimp in tempura batter, shaking off excess. Fry shrimp, in batches, 1-2 minutes on each side or until golden; drain on a wire rack over paper towels.
Serve in warm tortillas with the Mexican coleslaw mix and desired toppings.