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!

Introduction
This build is fairly interesting, and relies on two commonly overlooked aspects of the Necromancer's kit. The first being Maltorius' Petrified Spike, a legendary item that boosts your bone spear by 700%, and Bone SpearTeeth, a skill that sprays half the map in death and shoddy dentistry. The Spike itself has fairly terrible stats, but it's unique ability and enough intelligence make up for this aspect.
 
Gameplay and Strategy
This is a very easy build to execute and yields extraordinarily high results. It's more of a medium range build, with plenty of variance as it only relies on a small combo. The rest of the build is mostly just to optimize the amount that you can use Bone SpearTeeth and making sure you survive well, with a fair bit of boss killers, such as Command SkeletonsFrenzy and Corpse LanceBrittle Touch. You can alter the range and play style with substitutions, and overall this is a very solid and general build for beginners and experienced players alike. 
 
Your main combo rotation is going to be using  SimulacrumReservoir and spamming Bone SpearTeeth. Then follow up with Corpse LanceBrittle Touch to finish off any remaining units. Corpse lance does not consume any essence to cast, and is very resource efficient while still dishing out significant damage. You may ask, why pick these runes. Well, Reservoir provides more resource, Brittle Touch helps with higher health bosses, and Teeth is actually a bit complicated. Now this may be a bug, but it certainly seems like the splinters from Bone SpearTeeth do too much damage, especially when combined with Maltorius' Petrified Spike. Because of this damage, you can easily clear massive waves and bosses alike. 
Your other core skill is going to be Blood Rush. Every class ought to have a mobility skill in order to more efficiently clear floors and to speed up your farming. I prefer to use Molting to start a Corpse Lance chain in adventure runs, but the rune you choose is mostly up to preference. Potency is also a powerful rune, especially if you choose the close range variant of this build
 
Other skills include your essence regain, either Grim ScytheDual Scythes or Siphon BloodPower Shift.  I like Dual Scythes simply because its a larger area (and therefor more essence), pulls enemies in front of you, and efficiently lines up the highest damage Bone SpearTeeth. An alternative to Dual Scythes is Grim ScytheExecution or Grim ScytheCursed ScytheSiphon BloodPower Shift is an excellent choice for melting bosses when low on essence. Other options include Siphon BloodSuppress, Siphon BloodBlood Sucker, or Bone SpikesBlood Spikes. Your choice of basic attack will determine your range for this build. Keep in mind that Teeth does more damage close up (like a shotgun) but due to Maltorius' Petrified Spike you can still use it at a range to great effect. For your non-combo damage ability, you want to choose based on your range. If you choose Siphon Blood, pick Command Skeletons with either Frenzy or Kill Command. If you choose Grim Scythe, go with either Bone ArmorDislocation or Death NovaBlight. Death nova does significant AOE damage, while Bone Armor is primarily a defensive skill, especially useful to preserve your Blood Rush cooldown. I personally prefer Frenzy for ranged and Bone ArmorDislocation for a closer range build. 
 
Passives
Your passives will once again depend on your variant of the build. You will want Overwhelming Essence and Blood is Power regardless, but the other two slots will vary.  Overwhelming Essence and Blood is Power are both integral skills to any ability and cooldown-based build. You want to minimize your cooldowns, and despite the intimidating requirement of Blood is Power, it triggers rather often. It counts premitigation damage, meaning damage before your armor and resistances. In any high level battle, you will proc this passive often. Overwhelming Essence is rather straightforward, as it simply increases your resource. 
 
For the close range variant, I would recommend Stand Alone and Draw Life. Together, these passives will make you significantly more bulky and make up for a lack of sustain within your skills. An alternative to Draw Life is taking Life from Death and DevourSatiated over Corpse LanceBrittle Touch. This will somewhat lower your damage to bosses, but provide for more spam and sustain overall. 
For the range variant, I would Aberrant Animator and Final Service. These both combine nicely with your Command Skeletons, while Final Service helps to improve your general lack of tankiness. Aberrant Animator gives your skeletons double your Thorns damage, while Final Service is your cheat death mechanic. 
Skill list
A- Grim ScytheDual Scythes/Siphon BloodPower Shift
B- Bone SpearTeeth
X-  Command SkeletonsFrenzy/ Command SkeletonsKill Command/Bone ArmorDislocation/Death NovaBlight
Y-  Corpse LanceBrittle Touch
ZL-SimulacrumReservoir
ZR-Blood RushMolting/Blood RushPotency
 
Passives
Overwhelming Essence Blood is Power Stand Alone / Aberrant Animator Draw Life / Life from Death / Final Service  
Now, into the parts that honestly don't matter nearly as much. Most of the build is in your hands, now this is just the nitpicky optimizations that I will honestly spend far too much/little time on. For the next sections I will be discussing gear, gems, Kanai's Cube, and paragon points. 
For Gear I recommend going for a Legacy of Dreams build. This is rather standard, gives you an insane damage boost, and overall is versatile and workable. Make sure that you haveMaltorius' Petrified Spike. Another recommendation is your helm. Leoric's Crown is ideal for general battling, but Broken Crown is my preference for base gem farming, for hopefully obvious reasons. Honestly, just use common sense. LoD builds are incredibly player dependent, and you can build them just about however you want. Just prioritize whatever will feed into the general gameplan of spamming SimulacrumReservoir and Bone SpearTeeth. 
For Kanai's Cube, you want to slot in Reilena's Shadowhook as your weapon, Krysbin's Sentence for jewlery, and the worse of either Reaper's Wraps or Nemesis Bracers. Shadowhook scales your damage based on your maximum essence, and with Overwhelming Essence and SimulacrumReservoir you're pretty well maxed out on your essence. 
For Paragon Points you want to basically use common sense. This build is an ability spam build with limited sustain. Play to that. For example, you want to invest heavily into Essence, Cost Reduction, and Cooldown reduction. As far as defense, I recommend investing in armor so that Blood is Power is easier to proc. 
For  Gems you should put Bane of the Trapped, Enforcer, and Legacy of Dreams in your ring slots. Zei's Stone of Vengeance is a solid alternative. For your Helm, slot in  Flawless Royal Topaz to provide resource cost reduction or Flawless Royal Diamond for CDR. Personally, since this is a teeth build you should go Topaz. For your weapon, you should go Flawless Royal Topaz if going the ranged build, and Flawless Royal Emerald for the close range build. And for your other slots, you should go (you guessed it) Flawless Royal Topaz. In my honest opinion, Topaz is the best base gem for necromancer. It provides Intelligence, thorns, and resource reduction. Sure, the thorns are only especially ridiculous with Aberrant Animator but once again, topaz is a godsend for Necromancer. 
 
 
Changelog: 10/2/19 Fixed some grammar errors, clarified poor usage, and added more details to the build