In a medium bowl, combine shredded green and red cabbage, grated carrots, 2 tablespoons of lime juice, and chopped cilantro.

Whisk together mayonnaise, sour cream, 1 tablespoon of lime juice, garlic powder, sugar, and salt in a small bowl; then, set aside.

In a large bowl, combine flour, cornstarch, baking powder, garlic powder, paprika, salt, and black pepper. Gradually whisk in cold beer until a smooth batter forms.

Heat vegetable oil in a large deep skillet or Dutch oven to 350°F (175°C). Dip fish fillets in the batter, letting excess drip off, and fry in batches for 3-5 minutes per side until golden brown and cooked through; then, remove and drain on a wire rack.

Warm the corn tortillas. Fill each tortilla with fried fish, top with a generous spoonful of slaw, and drizzle with the creamy sauce. Serve immediately with lime wedges.