The Necromancer is a friend of the dead, able to exploit corpses for his own use. He is adept at summoning chaotic creatures at his side, enabling him to be effective without a group of players at his side, because after all; he often has an undead army watching his back. But his real strength is in his very potent curses, they allow him to passively deal extra damage or reduce the effectiveness of enemy creatures. Nevertheless, he does have a frail body and is not able to withstand much damage without suffering the ultimate defeat, death and as friendly as he might be with the dead… he cannot escape the long sleep.
Success will depend greatly on the use of summoning and curse skills, as they are the most effective available when dealing with large groups of monsters [which happen to be rather common in Diablo 2]. Iron Maiden happens to be one of the most useful curses available and don't forget to specialize in a golem. A blood golem is very useful, due to it's life being linked to your character, but do not overlook the fire golem because it is rather handy when reaching the tougher difficulty levels.
The Necromancer's History
As might be expected, the devotees of magic are a segregated lot. They are as leery of students of rival disciplines as a layperson is of all arcane practitioners. None, however, are so widely maligned and misunderstood as the Priests of Rathma.
As with most users of magic, the priests of the cult of Rathma hail from the far Eastern jungles. They reside in a vast underground city located deep within those jungles. Their specific geographical locale is particularly secluded, however, preventing their assimilation into a formal mage clan. But it is this same isolation that allowed them to pursue their distinct kind of arcane science. For it is through the teachings of Rathma, as well as through years of research and physical experimentation, that these men have come to understand and hold sacred the delicate balance of life and death and are able to twist the line that borders the two. For although the minions of Hell have long possessed this power, among mortals the knowledge to reanimate and control the dead belongs to these priests alone. It is this practice that has lead outsiders to refer to them as Necromancers. They truly comprehend the balance of all things, and understand and accept their place in what they refer to as the Great Cycle of Being.
Their culture has subsisted in the shadow of the great mage clans from the earliest days, and in most ways their practice reaches back to a time before magic was formalized into strict disciplines.
Although their art is considered "dark," and the people of the outside world shun the priests who practice these arts, these mysterious cultists never suffered the epidemic of corruption that plagued the ancient Mage Clans. Pragmatists in the truest sense, they are above temptation. They see death merely as a natural part of life and do not seek to deny its arrival. Their singular knowledge of the unknown allows them to face death without fear. These ideals, coupled with an understanding of the natural balance between Order and Chaos, explain why they have not fallen prey to the influences of evil.
Their desire to uphold this balance has brought the Necromancers forth from the isolation of their remote, dank homeland to destroy Diablo and his brethren. For the mere presence of these Prime Evils on the mortal realm upsets the natural symmetry of not only the mortal realm, but also the Great Cycle of Being, itself. The followers of Rathma seek to right the balance by ridding the mortal realms of non-mortal intervention altogether. They resent any force that would treat humans as pawns in a cosmic game, though they are apparently willing to ally with the forces of Order but only until such time as the balance is restored.