For the simple syrup
In a medium saucepan combine sugar and water. Bring to a boil, stirring, until Splenda Stevia Crystal has dissolved. Let it cool slightly.

In a blender, pulse the mango and mint leaves together with the lukewarm syrup, until roughly pureed.

In a cocktail shaker or jar, add ice cubes, mango puree, rum and lime juice. Secure lid and shake. Pour mixture into two glasses with ice, and fill the remaining glass with club soda. Top with mint and mango for garnish.