In a small pot filled halfway with water, bring to a boil over medium-high heat. Once boiling, add the tapioca pearls and reduce to medium heat. Boil uncovered for 10 minutes, stirring occasionally.
Turn off the heat, cover, and let the pearls sit in the hot water for another 10 minutes, until softened and mostly translucent. If you still see a small white dot in the center, cover and let them sit for an additional 2-3 minutes until fully translucent.
Strain the cooked pearls through a fine mesh sieve and rinse under cold running water until cool to the touch, removing excess starch. Keep the pearls submerged in water to prevent sticking, then strain well before assembling the drink.
Meanwhile, add the mango and sweetened condensed milk to a blender. Blend on high until completely smooth. Divide and spoon the mango mixture into two (12-oz.) serving glasses.
Add equal portions of the drained tapioca pearls to each glass, followed by 2-3 ice cubes. Set aside.
In a large bowl, whisk together the coconut milk, cold water, and sugar until the sugar fully dissolves. Pour the coconut mixture into each glass. Add ice, stir, and enjoy immediately.