Bring a medium pot of water to a boil. Add tapioca pearls and reduce heat to a simmer. Allow to simmer, stirring frequently until pearls are tender and transparent (25-30 minutes).
While tapioca is cooking, put half of the mango slices in a medium mixing bowl and mash with a fork until smooth. Add coconut milk and sugar and mix until combined.
Strain and rinse tapioca pearls with cold water. Add pearls to mango mixture and stir until pearls are evenly coated with liquid. Cover the bowl and allow to chill in the refrigerator for at least 30 minutes.
When serving, divide pearls between 4 bowls, top with slices of mango and drizzle a bit of yogurt over the top.