In a small saucepan sprinkle the gelatin over 1/4 cup cold water, let it soften for 1 minute, and heat the mixture over low heat, stirring, until the gelatin is dissolved. In a blender, blend together the mango puree, the sugar, and the vanilla, add the gelatin mixture and blend the mixture well. Transfer 3/4 of mixture to a bowl and stir in the yogurt. In a chilled bowl beat the cream until it holds stiff peaks, reserve 1/4 cup and fold the rest into the mango mixture gently, but thoroughly. Assemble and divide the mousse amount into 4 martini glasses placing 1/2 tablespoon mango slices and add a generous layer of mousse and another layer of the chilled cream. Chill the mousses for at least 4 hours or overnight. Garnish with mint sprigs or pomegranate seeds.