Capítulo 571: 9.05.3 The immortal serpent.

Rosso chose to spare the captain and the voodoo practitioner whose name he later learned to be Rodo. 

And it was not mercy that made him spare the Voodoo practitioner, it was curiosity. 

Voodoo is such a bizarre path that can incorporate curses and magic together. Two different energies would usually collide and destroy each other if they exist in a singular body. But Voodoo Practitioners, are somehow able to influence the curse energies around them using the magic in their body. 

Of course, they use countless materials and even souls of the death for this job, but the fact that they had been able to achieve what many mages can't, It's something to behold.' Of course, there is a reason why the majority of magic practitioners fail at it.'