In a small bowl, combine the mayo sauce ingredients and set aside.
In a large bowl, whisk together the rice flour, tapioca starch, flour, sugar, and baking powder. Pour in the cold water and whisk until mostly smooth (it's ok if there are a few lumps; you do not want to overmix the batter).
Heat 1 inch of oil to 375°F in a tall pot of your choice. Dip the shrimp in the batter, shake off excess, and gently lower into the hot oil. Cook 5-6 shrimp at a time for 2-3 minutes until brown and crispy. Transfer to a wire rack to drain excess oil.
Combine the fried shrimp and mayo sauce in a large bowl and toss to coat.