OK. I have built a L70 Necro. By way of introduction, I played D, D2 and D3/LOD for about 10 years. Then my wife introduced me to WoW, which I've been playing for the last 5 years. However, I didn't enjoy anything about Shadowlands so came back to D3.
I'm looking for a couple of things:
One, I have always played solo but find at this level I need a playmate. So if anyone out there is interested, drop me a line (Spoiler: I am an old guy but I love the game); Two, I want to discuss ideas about the Necromancer build, I don't understand how some of the skills work. I currently have (1) Army of the Dead, (2) Bone Spear, (3) Corpse Lance, (4) Command Skeletons, (L) Grim Scythe and (R) Siphon blood. It's a powerful semi-melee/ranged attack. It's worked well but I'm into Greater Rifts now and while I can complete them I don't get thru fast enough for the big rewards. So I would like someone to suggest if and how I can improve the build to address this (and why this will work better -- that isn't a challenge, I just need to expand my education.

I am going the corpselance support build for Necromancer and the build has me taking Corpselance with Brittle and the pestilence set on top of that, if I were to take off the ability Corpselance and change it to another ability say for example Bone Spikes with Frost spikes, would the damage decrease an amount that it would not be worth it?

I recently returned after a semi-long abscence/break and remembered I enjoyed the Necromancer Pestilence set with Corpse Lance, but couldn't quite remember the build, so I hit up the Necromancer Corpse Lance Build with Pestilence or Trag'Oul's set.
In the Skills and Runes section, it's mentioned that alongside Land of the Dead, one would also pick Simulacrum (3rd and 4th paragraph of "2. Skills and Runes"), yet the skill shows nowhere in the build's actual skills and between the stated skills to be picked, there's no room for it. Similarly confusing was the mention of picking the "Stand Alone" passive as it would "take full advantage of the lack of permanent minions on its side, and enjoys the full 100% armor bonus." - yet the build includes "Command Skeletons".
Am I missing something crucial or has the guide been reworked at some time and this was overlooked?
Thanks for any clarification!

Set myself a challenge to create a T16 viable funbuild with some rarely used legendary gems and here it is 💝
Of course Mirinae, Teardrop of the Starweaver and Gem of Efficacious Toxin can be easily switched for things like Bane of the Stricken or Bane of the Powerful to make build viable for even higher Rifts, but that wasn't really the point 🦄
I like not having to cycle through too many buttons so that's why I picked two aura runes.
I personally don't have the seasonal 4th cube unlocked, but I think the best option would be to add Reilena's Shadowhook for an added damage buff.
In terms of Paragon Points, I'd just max movement speed and essence increase and then put everything in intelligence, since the build is very sturdy and you shouldn't struggle with survival once you hit 15 stacks of Bone Armor at all. Like with every Grace of Inarius build though, you need to be careful when when you're low on stacks, but keeping them at 15 at all times shouldn't be a problem.
Since it uses both the Inarius and Aughild sets with Ring of Royal Grandeur, the set items used can be swapped to personal preference as long as both are active.
Items:
Head: Aughild's Peak
Chest: Inarius's Conviction
Shoulders: Inarius's Martyrdom
Bracers: Aughild's Ultimatum
Gloves: Inarius's Will
Belt: Dayntee's Binding
Pants: Inarius's Reticence
Boots: Inarius's Perseverance
Amulet: Wisdom of Kalan
Ring1: Krysbin's Sentence
Ring2: Lornelle's Sunstone
Weapon: Jesseth Skullscythe
Off Hand: Jesseth Skullshield
Active Skills:
Grim ScytheCursed Scythe
Command SkeletonsFreezing Grasp
Command GolemBone Golem
Bone ArmorDislocation
FrailtyAura of Frailty
DevourDevouring Aura
Passive Skills:
Fueled by Death
Spreading Malediction
Commander of the Risen Dead
Rigor Mortis
Legendary Gems:
Mirinae, Teardrop of the Starweaver
Gem of Efficacious Toxin
Red Soul Shard
Bane of the Trapped
Kanai's Cube
Trag'Oul's Corroded Fang
Aquila Cuirass
Ring of Royal Grandeur
Reilena's Shadowhook
 
The general principle is to soften enemies up with Inarius, Gem of Efficacious Toxin and a barrage of debilitating effects to make the damage output from Mirinae, Teardrop of the Starweaver and Red Soul Shard actually significant.
Questions, experiences, suggestions and love letters are always welcome!

Alright my first build... Here we go!
Now Necromancers aren't my 'main' classes but i play with them and im pretty good with them. And i come up with a build that is a bit boring, but ultra powerful, so lets begin!
1. Primary Attack, Primary attack should be bone spikes with the rune: Path of bones or Blood spikes. Why? Blood spikes are for people that lose health really quickly, and the blood spikes allow you to heal over the bleeding enemies you hit. Path of bones on the other hand is for people who have a lot of enemies in your way. Or you can have no rune, which i mildly recommend for people who are already strong just want to be a bit stronger :))
2. Secondary Attack. Should be Bone spear with the rune: Teeth or Blighted Marrow. Teeth is the one that i recommend for most people to use, why? Teeth fires more bone spears trough enemies, of course it deals not much damage but it damages more enemies. Plus, you can get an achievement for killing 40 enemies with bone spear within 3 seconds. Bligthed Marrow is for people that like to stay behind their minions and just fire their bone spear trough enemies. I call this build the lazy one. 
3. Corpses. Should be using Corpse Lance with the rune: Ricochet. Why? Ricochet allows you to have an chance to hit one more bonus enemy when you attack the first one. Which is pretty good.
4. Reanimation. Should be Command Skeletons with the rune: Kill Command,Frenzy and Dark Mending. Kill command is for people who are confident without their minions and want ther minions do yeet themself to enemies and kill them in one shot. Frenzy is the one that i recommend the most, this will allow you to command your skeletons to gain attack speed (which means more damage to the enemy) and it's just really that powerful. And Dark Mending is the last one. Dark mending is for people who lose health pretty quickly and want their minions to heal them.
5. Curses. Either Frailty or Leech. Frailty is for people who want their minions to deal much bigger damage with the rune: Scent of Blood. Why? Scent of blood will allow your minions to attack 15% increased damage, which is really helpful if you want your minions to do the job and not you. Leech is for people that lose a lot or a bit of health. With the rune Sanguine End. Cause it will allow you to heal 200% for the enemies that die.
6. Blood and Bone. This should be RIGHT OF THE BACK bone spirit with the rune: Poltergeist. Why? Bone spirit is powerful as heck and you should use it immediately when you get it. The rune Poltergeist will allow you to have 4 bone spirit, which means EVEN MORE DAMAGE THEN BEFORE HAHA.
7. Passive skills. I recommend: Overwhelming Essence for people that want more Essence and use a lot of Essence now and then. Spreading Malediction is for people that want their curses to deal a lot more damage, well not much but 1% increased damage is at least okay. Serration is also a really good passive skill, Serration is for people that like to stay behind while their minions do their business and you like to stay behind and just shoot bone spikes at them. And finally Aberrant Animator. For people that like to increase the thorns damage for their minions
And that's it! Took me a lot of time, and some repilies and thanks would be appreciated. And yeah, hope you are good with your necromancer now!
OH sorry if the text is black! I didn't realize that it would be hard to read on my post, cause when i m editing it looks white so... sorry :((