Preheat oven to 350 degrees Fahrenheit. Grease and flour a 9x13-inch baking dish. In a medium bowl, combine the biscuit mix and sugar. Add the sour cream, eggs, milk, and vanilla extract and mix until just combined. Fold in the blueberries. Pour the batter into the prepared baking dish. In a small bowl, combine the sugar, flour, and butter. Use your fingers to work the ingredients together until the mixture resembles coarse crumbs. Sprinkle the crumb topping over the batter. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.