1. Coarsely chop 2 mangoes. Dice the remaining mango.
2. Combine coarsely chopped mangoes and 1/4 cup water in a blender; process until smooth. Press puree through a fine sieve over a bowl; discard solids.
3. Bring 3/4 cup water to a boil in a medium saucepan. Add sugar to pan, stirring until dissolved. Remove from heat. Stir in the remaining 1 1/4 cups water. Sprinkle unflavored gelatin over water in the saucepan; let stand 1 minute. Add the mango puree, stirring with a whisk. Pour the mixture evenly into each of 8 (6-ounce) ramekins or custard cups. Cover and chill overnight or until set. Top evenly with diced mango.
4. Place cream in a medium bowl; beat with a mixer at high speed until stiff peaks form. Serve with pudding.