Care to share your experiences with the Necromancer?
Even on harder difficulties, the character can be overpowered based on how many passive summons one can get.
My primary Axe-style weapon can auto-summon a powerful ghostly Legendary Ogre warrior (disappears after a battle ends).
Next, I use my special to bring back fallen enemies from the dead---they fight for you and follow you continually.
Lastly: I can summon undead magicians or summon skeletal warriors (up to 8 I believe), that will fight endlessly and you can boost into beserk mode PLUS they can heal you.
As a Bonus, combine all that with heal on bleed ability / accessories---so with any damage your minions cause, you gain back health. Ultimately, I'm never in any real danger on Hard / extreme difficulties, often holding a near-endless army behind me.
What are some of your tactics or play styles around this character?