Simmer the water, sugar, and mashed raspberries 3 minutes. Strain, stir in the lemon juice, and cool.Beat the mascarpone, powdered sugar, and vanilla until smooth. Add the cream and whip to stiff peaks.Lay a long sheet of plastic wrap on the counter or use a long platter.Quickly dip each ladyfinger in the syrup, 1 second per side.Line up 8 dipped ladyfingers side by side. Spread with cream and scatter with berries.Add two more layers of ladyfingers, cream, and berries, pressing gently.Spread cream over the top and sides. Refrigerate at least 6 hours or overnight.Top with fresh berries, mint leaves, and a dusting of powdered sugar before serving.