Drain mango slices, reserving 1/2 cup juice. Place mango slices and reserved juice in a bowl. Beat with an electric mixer until pureed.
Bring 2 cups water to a boil in a large saucepan. Add gelatin; stir quickly until dissolved. Pour in sugar and stir until dissolved. Add remaining 1 cup water. Remove from heat and let cool, about 5 minutes.
Mix pureed mango and 2 cups plus 2 tablespoons heavy cream into the water mixture; mix well. Pour into 8 dessert cups.