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 :((

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    

All credit goes to Wrechanoth @ DiabloFans.com: Link <--Direct link to Build
I have been using this build since the Necromancer was released
 
Nowhere near mid-tier build, but fun to play and fairs pretty nicely when completing season journey.  
 
 

This build plays upon the strengths of Trag'Oul's 6-Piece set while also granting huge mobility.  Every part of this class plays well with each other.  Your Bane of the Trapped along with Krysbin's are going to be proc'd heavily due to your constant stuns.  Your Lornelle's is going to benefit from the health drain of the Skeleton Mages, who in turn benefit from Trag'Oul's 6-piece set bonus.  This is a generator-less class.  Your essence will instead come from Devour and picking up health globes.  Because of this, it might be suggested to re-roll some of your pieces to increase the range at which you can pick up health globes.  All in all, this is a fast trash and elite clearing build that will allow you to speedfarm/speedbounty/speedrift without much trouble.  There are lots of trade-offs in damage for increased survivability, speed and mobility.  As such, this build is not suitable for GR progression. 
Gear And Cube
Weapon: Jesseth Skullscythe
Off Hand: Jesseth Skullshield - We want the set bonus from having both of the Jesseth items equipped.  Command Skeletons is going to be your main "attack", as it allows you to focus your pets on a target.  Having this set bonus keeps your skeletons commanded as long as there are enemies on the screen, and it powers up your Skeleton Mages.
Belt: Krelm's Buff Belt - For the speed buff.  If movement speed is less important to you than damage (for example, if not playing on Season 16), then you can replace this with The Witching Hour.
Wrists: Reaper's Wraps or Nemesis Bracers - The Reaper's Wraps are are craftable.  I'd recommend these for running bounties/goblins.  For speedrifting, go with the Nemesis Bracers.
Head: Trag'Oul's Guise
Chest: Trag'Oul's Scales
Shoulders: Trag'Oul's Heart
Hands: Tasker and Theo or Trag'Oul's Claws - Use T&T if playing on Season 16, otherwise take the Trag'Oul's.
Legs: Trag'Oul's Hide
Feet: Trag'Oul's Stalwart Greaves
Ring One: Krysbin's Sentence - This will proc nearly all the time with this build.  Super powerful ring.
Ring Two: Lornelle's Sunstone - This is an odd take for most builds, but with a good roll, you can get +Int, +CHD, and +CHC as well as pretty great damage reduction on this ring.  For that purpose, this ring is mandatory.
Neck: Wisdom of Kalan - This could be substituted for a more damage-focused neck, like The Johnstone or a Hellfire Amulet with good stats and a good passive.  The extra 5 stacks of Bone Armor will help our movement speed, however.
Cube Weapon: Scythe of the Cycle - Straight up Skeleton Mage buff.
Cube Armor: Steuart's Greaves - If not playing Season 16, you could put Tasker and Theo here.  However, the movement speed buff is incredible.
Cube Jewelery: Circle of Nailuj's Evol - Another big Skeleton Mage buff.
Skills and Runes
Left Click:  Bone Armor, with the Dislocation rune.
Right Click: Blood Rush.  Rune doesn't matter, since Trag'Oul's will give you all of them.
1: Skeleton Mage, with the Life Support rune.
2: Command Skeletons, with the Frozen Grasp rune.
3: Land of the Dead, with the Frozen Lands rune.  I hardly use this in my runs, as it's not really necessary.  It's more of an "oh *filtered*!" skill I use in emergencies.  That said, this is great against bosses.
4: Devour, with the Devouring Aura rune.  Your biggest essence generator.  The rune just makes it easy to manage, but if you like pressing buttons constantly, take the Cannibalize rune.
Passives: 
1: Dark Reaping
2: Grisly Tribute
3: Overwhelming Essence
4: Final Service
5: Extended Servitude - Only take this if you've got a Hellfire equipped that gives you one of the above passives.
Stats:
Int should be your main stat.  The following three stats are my recommended priorities in order after Int: +%CHC, +Armor, Gold/Health Pickup range increase
Paragon:
Paragon Priority should be :
Core: Movement Speed > Intelligence > Maximum Essence > Vitality
Offensive: Crit Chance > Crit Damage > Cooldown Reduction > Attack Speed
Defensive: Armor > Resist All > Life Regen > Life
Utility: Life Per Hit > Resource Cost Reduction > Area Damage > Gold Find
Gems:
Helm - Diamond
Chest - Two Topaz, one Amathyst
Legs - Two Topaz
Weapon - Emerald
Anything not jewelry - Topaz
Jewelry - Bane of the Trapped, Enforcer, Bane of the Powerful
Playstyle:
This build has an odd playstyle.  Aside from the small output of Bone Armor, you are not going to do any damage directly.  You're going to pop Blood Rush as much as you want to zoom around the map.  When you encounter enemies, you want to get near them and pop Bone Armor.  After that, Command Skeletons to one of the enemies (you can pop this multiple times per encounter.  Whoever you target with this will become your damage priority.  Then pop exactly 5 Skeleton Mages.  While your pets do the work, Blood Rush around the pack of enemies in order to Devour corpses to restore your essence.  Pop Bone Armor as it becomes available. 
Just do this from pack to pack and you'll be fine.  I've been able to clear Act II bounties in less than 7 minutes, a Golbin Farm run in less than 4, and a regular rift in under 2.  This is all on T13, by the way.  I am Paragon 590 as of the writing of this post.
If you find that you aren't doing enough damage, remember to make sure that your Skeletons are always Commanded.  If you don't command them, you're losing out on the damage bonus granted by the Jesseth set.  Also, make sure you keep 10 Skeleton Mages up at all times.  This equates to casting it 5 times, if you have Nailuj's Evol cubed.