Necromancers are not very strong individuals, by their nature. Their three skills are Summoning Spells, Poison and Bone Spells, and Curses. They start out with a dinky little wand, but it allows you to Raise Skeletons at Level 1. Now, tell me something. You kill a Quill Rat and you get ... a human skeleton out of it? How in the world does this happen? Ah well.
As you add to the Raise Skeleton skill, you can control more skeletons at a time. A whole horde of Skeletons! A plethora of Skeletons! Skeleton Mastery is another good one, to strengthen those skeletons up.
You should also grab Bone Armor which pays mana to animate skeletons around you, absorbing damage that was aimed towards you. That is in essence your "healing" aspect - so you should also grab items that heal actual damage, and carry potions with you. It's not until 18th level that you get Life Tap which sucks damage from an enemy as health to you.
Necromancers have cool spells, like Attract at 24th level - you cast it on a monster and everyone else attacks it. On the annoying side, the creatures the Necromancers control aren't very obvious - if you're playing multi-player, those extra skeletons often get in the way and block doors and such.
Diablo 2 Walkthrough
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