With a very hard mango you basically just cut ‘v’s into the skin slightly higher than the previous ‘v’ but at the same angle to look like the cone is tucked under the previous piece and cut away some flesh to leave a little green. Here is a quick look at the chef doing it.
This is fairly simple once you understand you want the ‘v’s to be up a little. you can do the same thing on a carrot (no dodgy comments Jono!!)