The Necromancer is one of 6 playable classes in Diablo Immortal.
"The priests of Rathma seek to bring balance to the world. They use their powers over life and death to keep Sanctuary free of both demonic and heavenly influences."
Necromancers are masters of raising the dead to fight by their side. Typically, Necromancers stand back behind an army of mindless minions who do engage the enemies for them.
It is not know at this time what abilities Necromancers will have in Diablo Immortal.