Level with Orb of Storms/Stormblast Mine/Frost Bomb until Level 28 and then swap to Cremation + Armageddon Brand. Stick with Cremation + Armageddon Brand until level 55+ AND when you have access to Vaal Detonate Dead.
Run Arctic Armour before Grace/Freeze immunity pantheon upgrade.
Gravicious unveil/craft on chest for 10% Life as Extra Maximum Energy Shield craft (important for ghost dance!).
Keep Vaal Detonate Dead at level 1 to reduce mana cost (only gains AoE with level so not worth levelling up).
When you swap to Detonate Dead make sure you have Raise Spectre Gem Level 13 to raise 2 Spectres total. Spectre options listed below!
I start by using Auto Enforcer + Rusty Crusher from Tunnels/Repository Heist contracts. Auto Enforcer needs lockdown to spawn.
Best Endgame Spectres are called Stoneskin Flayer and Lithomancer found in the Primeval Ruins in Delve (Aul city, no Aul required just a city).
More spectres listed in this pastebin link, useful for corpse dilution (open this pastebin link in browser!)
https://pastebin.com/YBGDGKf4
Can bring in additional spectres within an instance to increase chance of desecrating them for additional damage (AKA Corpse Dilution).
I use a level 28 Spectre Bank with Queens Decree and Death Attunement on the passive tree to hold onto 3 spectres which I can use to spectre them on my main character by entering hideout and relogging.
Guide from Ziz here -->
https://www.youtube.com/watch?v=wAlUGv0s9wQ
(Note: You need to level the characters manually to 28 as PvP characters don't work anymore but the concept is the same).
---------------Extra tips---------------
The build works by casting desecrate and detonating the corpses that you spawn. To deal single target damage you need to detonate high life corpses which can be spawned using desecrate with high life spectres summoned (such as Rusty Crusher
+ Auto-Enforcer). To maximum single target we also have lots of ailment duration combined with carefully timed Vaal Detonate Dead usage to achieve large ignites that last 12+ seconds. Area + zone level will dictate your damage, you effectively
deal similar damage in a 68 zone as an 84 zone because the corpse life scales with zone level.
Make sure your desecrate is levelled, you need a lvl 19 desecrate for 81 and below zones and a lvl 20 desecrate for anything beyond that.
Focus Ailment Duration mod on helmet is EXTREMELY noticeable for longer lasting ignites, get this for endgame bossing.
Ungil's is used for proccing Elemental Overload (gives a lot of crit) but you can replace this with the Inquisitor version or by using a combination of the extra crit chance spell suppression mastery, crit enchant on boots and spell crit on weapon.
Main difference between necromancer, inquisitor and elementalist is as follows: Necromancer has a balance of defence and damage but lacks recovery, Inquisitor has defence and recovery but lacks damage, and
Elementalist lacks defence and recovery but has the most damage.
You can ditch the desecrate + spectre setup with an unearth setup instead but you need empower + enhance + alt quality phantasmal unearth in a +1/+2 gems item (such as Hands of the High Templar or Viridi's Veil)
and a +5 corpse unearth level enchant.
