This allows melee builds, summoners with skeleton fighters dealing physical damage, summoners with skeleton mages dealing elemental damage, golem-mancers who focus on powerful golems to pair with the merc, summoners that focus on reviving dead enemies to fight with the necro, poison spell casters, bone (magic) spell casters, and back to melee with any combo of summons. The Summoning tree provides multiple options for minions the Poison and Bone tree allows powerful poison damage, magic-based bone damage and defensive spells, and the all-powerful Corpse Explosion that brings area-of-effect fire and physical damage and the Curses tree allows complementary spells that enhance damage or provide major crowd control. The Necromancer probably has the most variability of possible builds among the Diablo 2 character classes.
Other Stats – Resists and Faster Hit Recovery.