Being a Necromancer demands great Intelligence and Charisma, along with minor Endurance.
How to Unlock
Go to the Mage Academy Tower, and speak to a student near the headmaster who mentions a crypt where all the cool kids hang out. The crypt (called the Forbidden Library on the world map) is North by Northeast of the Mage Tower. Make your first right (southeast), take a left (northeast) when you can, and then keep heading straight to find the Skull of Necromancy; you can do this even with starter gear if you run past all enemies (otherwise the official recommended lvl is 8). With the Skull in your possession, return to the Mage tower and you will encounter the Necromancer trainer in the headmaster's chamber.
Note that the Necromancer is not a good class for endgame, as most of the skills have no effect on bosses. However, Wandering Plague is a great boss skill because the poison does not run out ever.
WARNING: If you return to the Necromancer trainer in the headmaster's chamber, you will have the option to kill him again. If you do so, the Necromancer trainer in the Capital will disappear and you cannot train any more Necromancer skills!
|Raise Skeleton||Manifest a skeleton warrior for 10 seconds from the remains of a fallen enemy. You can have multiple skeletons, though you can't exceed 5 companions.||1 sec||
|Tainted Blood||Increases your resistance to both holy and unholy damage by 25%.||Passive||
|Wandering Plague||Applies an everlasting poison to your target. When this target dies, the plague can transfer to other nearby foes.||30 sec||
|Withering||Increases the critical strike chance of all periodic damage effects by 10%.||Passive||
|Summon Mummy||Conjures a powerful mummy, which is highly durable and deals heavy damage.||15 sec||
|Corpse Explosion||Up to 3 nearby corpses explode violently, dealing fire damage to their still-living allies.||10 sec||
|Army of Doom||Increases the health and duration of your summoned minions by 50%.||Passive||
|Dark Harvest||Destroy a nearby corpse and consume its life energy, healing you. (fallen Skeletons from Raise Skeletons also work)||10 sec||
|Cursed Knowledge||Increases the damage you deal to undead creatures and constructs by 15%.||Passive||
|Mass Hysteria||Your target and all surrounding enemies are consumed by madness, attacking each other for 6 seconds.||30 sec||
|Soul Mass||Generates a cloud of malevolent spirits which seeks out and explode upon the nearest enemy, dealing unholy damage.||12 sec||
|Aura of Disease||You are surrounded with a cloud of infection which deals poison damage to all nearby enemies.||Passive||
|Slay Living||Attempts to instantly destroy your target. If the effect fails, the target instead takes minor unholy damage. Ineffective on all bosses.||15 sec||