In a small saucepan, combine the dried hibiscus with 2 cups of water and bring to a boil. Then reduce heat to low and steep for 10 minutes covered. Use a fine-mesh strainer to strain the hot liquid from the hibiscus leaves and let it cool.

Add the blueberries to a blender and blend on high for 30 seconds. Pour blueberries through a fine-mesh strainer into a pitcher. Mix in 3 cups of chilled water, lime juice, and agave, and stir well. Taste for sweetness. Serve agua fresca in a glass with crushed ice and garnish with extra blueberries and mint.