This would feed on Trag’oul’s Avatar 4 pieces and 6 pieces.
While at full Life, overhealing from skills is added to maximum Life for 45 seconds, up to 100% more (4 pieces)
All Life-spending abilities deal 3800% increased damage. Healing from skills is increased by 100% (6 pieces)
While we could imagine an item granting Dark Mending to heal Necro…
Skeletal minions will heal you for 0.5% of your total health per hit while being commanded.
https://us.diablo3.com/en-us/class/necromancer/active/command-skeletons
…Bloodsong Mail already provides this power against Land of the Dead:
While in the Land of the Dead, Command Skeletons gain the effect of Enforcer, Frenzy, Dark Mending and Freezing Grasp runes and deal 100% - 125% additional damage.
https://us.diablo3.com/en-us/item/bloodsong-mail-P6_Necro_Unique_Chest_21
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Basic Stand Alone grants you 100% - (7 Skeletons * 10%) = 100% - 70% = 30% armor increase
200% Stand Alone grants you 200% - (7 Skeletons * 10%) = 200% - 70% = 130% armor increase
You’ll notice that Stand Alone acts on armor.
But armor comes after damage reduction.
About damage reduction, I debuffed Bone Armor but gave a basic, permanent damage reduction of 50% which should help when starting rifts, when you revive in the middle of enemies, or against rift guardian. You can still use Bone Armor on top of that and it will scale with the number of enemies hit by Bone Armor.
- 4 pieces : 50% damage reduction (permanent)
- Bone armor : 3% damage reduction x 10 enemies (60 seconds)
- Wisdom of Kalan : 3% damage reduction x 5 enemies (60 seconds)
Maximum : 0.5 + (0.5 x (3 x 15)) = 0.5 + 0.23 = 0.73 = 73% damage reduction
That should be enough 
I’m not sure that additional armor is required, since { Bone Armor / Dislocation + Ancient Parthan Defenders } can add damage reduction on top of that
https://us.diablo3.com/en-us/class/necromancer/active/bone-armor
https://us.diablo3.com/en-us/item/ancient-parthan-defenders-Unique_Bracer_102_x1
We could put a condition on granting the 4 pieces bonus (50% damage reduction), but the main complain of players is to not have a condition.
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Once equipped with Jesseth, Bone Ringer in the cube acts as the two handed weapon.
I’d say the mechanic already exists, but is just unused because base Skeleton is currently negligible. If Skeletons damage is buffed, Bone Ringer will shine again.
Right.
I once proposed an all-in, full bleed mechanic
https://ibb.co/m0V9Hn6
I just remembered that some players emitted observations on damage-over-time for their speed builds, as damage-over-time does not tick fast enough for this purpose.
On the contrary, lazy builds are OK with damage-over-time.