Before we start, this is very much still a work in progress guide, I've completed all 4 acts with the necromancer however still missing some skill unlocks. I'm very open to both feedback and build suggestion/recommendations.

I've also released a complete guide for both the Rogue and the Warrior,
feel free to check them out:

Complete Rogue Guide
Complete Warrior Guide

The Necromancer is unlocked by building a crypt.

While playing the necromancer you'll be able to equip 2 rings, 1 amulet, a book
and a shield (if you've placed an Arsenal card which is a gold card.)

Max Skeletons:
Increases the amount of total skeletons you can have active at once.

Summon quality:
Increases the chance of higher tier skeletons being summoned instead of the basic skeleton. So far I've experienced 5 different types of skeletons, those being in the following order:

1. Friendly Skeleton - Your basic melee skeleton
   
   
   
   
   
2. Warrior Skeleton - High damage, low HP
   
   
   
   
3. Skeleton Guard - High HP, low damage, has the trait "First target" which will force enemies to target it first.
   
   
   
   
   
4. Archer Skeleton - Support minion (They don't take damage), these will be summoned after reaching the max (4) number of melee skeletons have been summoned.
   
   
   
   
5. Skeleton Mage - Support minion (They don't take damage). Has the same stats as the Skeleton Archer however they do magic damage which is better against some enemies. They spawn like the archers after filling all the melee slots.
   
   

Skeleton level:
Increases damage and HP of skeletons.
Notice this does not do anything for your current summons. Only new ones.

Stats in order of importance is:

Skeleton level > Max Skeleton (3-4) > Skeleton quality > Max Skeleton (*)

The Necromancer will be able to receive the following stats on their gear:

• Attack speed
  
• Evade (%)
  
• Summon Quality
  
• Regeneration
  
• Defense
  
• Skeleton level
  
• Max Skeleton

Please do also note this is based on my personal experience. Some traits are only great when paired up with others. Some people prefer other traits than the ones I do, which is completely fair. This is just my current personal ranking. A lot of people seem like like Laying down one's life more than I do which also is completely fair, to each their own.

Reasoning for placements on the tier list:

Field practice - S
Allows you to stack Skeleton level which is just a very powerful stat on the Necromancer, boosts both health and attack of your skeletons.

Unseen care - S
Infinitely stack energy armor on a Necromancer vs Training dummies. Keep some low level gear swap it out as you run into a Training dummy village, they won't attack you if you don't attack them. Your skeletons will suicide over and over while attacking the training dummies. So you can keep respawning them resulting in as much energy armor as you want.

Lightning Fast - A
It's just additional damage for your skeletons, can really be used with any build.

Art of Control - B
It's an additional skeleton, allows you to save a stat slot on a piece of gear.

Laying down one's life - B
This is very good in any build focusing on attack speed. However to start spawning Skeleton guards doesn't take much Skeleton quality and if that happens then this will end up being useless.

Horde - B
Pair this up with Ambitions of the dead and you'll have some very powerful skeletons every loop.

Preparation for a ceremony - C
Really only useful when playing with Temporal beacons.

Residual heat - C
Great if you pair it with high attack speed and Laying down one's life, will keep you alive.

Counterattack - D
15% seems fairly low, have really not found much use for it.

Edge of impossible - E
I've placed this so low because it's only during the last summon. Had that part of it been removed this would have been great.

Omicron's Technique - E
While this might save you every now and then it wont make you any stronger.



Art of Control
+1 to maximum number of skeletons.





Edge of Impossible
20% chance to exceed the number of skeletons and summon 2 of them during the last summon.




Field Practice
+ 0.25 to skeleton's level for a loop (starting from the loop when this trait was received)




Preparation for a ceremony
First two skeletons summoned in a day will be strengthened.





Horde
3 strengthened skeletons will be joining the hero on every loop to help in battle





Residual heat
Receive +3*loop hp after skeleton's death.





Unseen care
A permanent +0.5 bonus to energy armor for every summoned skeleton.





Counterattack
After hero receives direct damage all skeletons have a 15% chance to immediately perform a counterattack.




Laying down one's life
Any direct damage to the hero will be evenly split between him and his skeletons.





Lightning fast
Summoned skeletons have a 20% chance to perform a quick 3-hit combo, with each hit dealing 50% damage. - Not Necromancer exclusive




Ambitions of the dead
After killing an enemy, skeleton fully heals itself; its damage and hp are increased by 10% until the end of battle.




Omicron's Technique
+1 resurrection charge - Not Necromancer exclusive

Feel free to post your build idea in the comments, I'll be trying out different builds as I play and will feature builds I have success with here.


Provided by Jabroni

The Thick Necromancer focuses on stacking as many Thickets as possible to boost the summon speed while using Laying down one's life, Residual heat and Unseen care to stack energy armor. Focusing on a single stat, Skeleton level to boost both the damage output and hp of the infinitely respawning skeletons.

Traits:







You'll wanna look for: Unseen care, Field practice, Residual heat and Laying down ones life.

Required buildings:
Only required building is Forest / Thicket which is unlocked by building a Forest in your base. Ancestral crypt should also be considered, however I've got yet to try that over the Arsenal.

Stats:
While focusing almost purely on Skeleton level you'll wanna get 4-5 total summon slots to split the damage from Laying down ones life. Can be done with either gear or picking up the Art of Control trait.


Provided by lyravega

Necro must-haves:

• Attack speed, through "Thicket" & "River" cards
  
• As many skeletons as you can get, without sacrificing much
  
• "Residual Heat" & "Laying Down Ones Life" traits
  
• Something that increases your max health or shield over time (Artifacts, "Ancestral Crypt" card, "Unseen Care" trait) to benefit in the mid & late loops
  
• Some "Skeleton Quality", anything but 0%

On later loops (loop 20+):

• "Skeleton Quality" & "Max. Skeletons" on pretty much every item
  
• Map full of "Thicket", in fact, skip all the "Forest" right from the beginning

Optionals

Beneficials:

• Suburbs

Faster level up

• Arsenal

The sooner you can get a bigger horde, the better

• Art of Control

Offers immense flexibility on item choices

• Lightning Fast
  
• Counterattack
  
• Blood Lightning

To simply put, extra damage

• Edge of Impossible

Chance isn't important when your skeletons start getting destroyed left and right. Summoning two at once might change the pace of the battle all of a sudden, it's actually useful.

Meh:

• Field Expedition

It might look nice, but it is per-loop, and it won't make a huge difference. Items start to get crazy as loops go on

Avoid List:

• Ambitions of the Dead
  
• Preparation for a Ceremony
  
• Horde

All of these traits are somewhat useless beyond first few loops, heck, they're even useless even in the first loops. If you aren't offered something else that might benefit you on the long run, I'd say launch another expedition

Energy armor:
It's a shield that will refill every fight, can be obtained through Unseen Care or the amulet slot.

Crunchy company (Achievement)
To achieve the Crunchy Company achievement all you've gotta do is place a bunch of cemeteries close to each other, as the achievement only states "Have 10 living skeletons in one battle." -Not which side of the fight they're on. Get a couple of +1 skeleton pieces of gear and you should be good.

Special tile Interaction:
Outpost:
A tile that normally will help you fight enemies in exchange for some of the gear that drops will as a Necromancer result in you also being attacked by the Outpost guards.

Forest/Thicket:
The forest tile increases attack speed, however as a Necromancer it'll increase your summoning speed. It is very powerful to stack a bunch of Thickets (2% Attack speed) tiles.

Jabroni
for their great insight on a Laying down one's life build, I had originally clearly placed it way too low on my tier list.

DegenerateGnome
for infinite magic armor stacking method. I was already aware of it but had forgotten to add it to the guide.

They also pointed out that placing the Outpost card as a Necromancer will result in the guards attacking you and the enemy instead of just the enemy.

Konstamonsta
for some useful insight on some trait combinations and for pointing out that I had forgotten to point out that Mage Skeletons do magic damage.

lyravega
For their generally good guidelines to play the Necromancer while trying to get into the higher loop levels of the game.