Put the frozen mango lime juice simple syrup and cold water in your blender.
Blend on high speed. Keep going until its smooth and looks like a thick slushy (about 30-60 seconds).
Check how thick it is. Too thick? Add a little more water blend quick. Too thin? Add more frozen mango or a few ice cubes blend quick.
Taste it. Does it need more sweetness? Add a bit more simple syrup and blend for a second.
Pour into chilled glasses right away.
Add a lime slice or mint leaf if you like. Serve immediately and enjoy!