My biggest question about all of this: Druids are all about nature, balance, etc... However, when we see a thematic element in a class, we also often see versions appear in antithesis to the core concept. Anti-paladins or Oath Breakers, for example. Where are the dark druids that animate dead and oppose the natural order? Where are the anti-druids?
In my setting, druids are tied to the Weave of magic that originates in the Positive Energy Plane and flows through all things until it reaches the core of the Negative Energy Plane. Powerful druids strive to bring balance to the Weave - and as the forces of darkness are usually ahead in the battle of good and evil tied to the Weave, they tend towards the magics of more positive energies ... now. However, in times of great prosperity in the past where the forces of darkness were at risk of being stamped out, the Druids found their role to require them to blight out the Light, embrace the Dark and show nature's ability to consume, destroy and kill. Some (a homebrew subclass) of those druids did this through becoming Anti-Druids, effectively, and animating the dead. Some used pure necormancy, others used spores like mycanoids, others corrupted fey and forced them to possess corpses. While these buggers are rare in the 'modern era' of my campaign, there are a few ... and when I use them as villains, they tend to be really popular with my players. The necromancer druid is an archetype that D&D has not done that much around, but it really works cohesively in the way that Anti-Paladins did for decades.
Critical Role has the Circle of the Blighted. That touches on dark themes, but not raising the dead. Circle of Spores can animate dead weakly - once they get to 6th level they can make 2 to 6 zombies ... but they each last only an hour and you have to wait for a long rest to bring them back.
That is not enough to build a necromancer style archetype around. I built a homebrew subclass that enacts my goals - primarily intended for use by NPCs.
Circle of the Dark -
2nd level: Your ties to the dark and undeath infuses you with the ability to cast certain spells. At 2nd, 3rd, 5th, 7th, 9th, 11th, 13th and 15th level you gain access to circle spells connected to undeath and shadow.
2: Find Familiar (see below), Shadow Veil* (All nonmagical light sources within 100 feet of your location are reduced - bright light becomes dim, dim becomes nonmagical dark, upcast to increase radius impacted by 20 feet, 1 hour duration, no concentration, immobile, spell not blocked by barriers)
3: Phantasmal Force, Death's Dark Mask* (Like Darkness, but upcasting increases radius by 5' - can't be cast on a moveable object)
5: Animate Dead*, Speak with Dead
7: Wall of Bone* (a weaker version of wall of thorns - but with bones - upcast similar to wall of thorns), Wraithform (similar to fly, blur, freedom of movement and able to go through small openings for 1 minute, concentration)
9: Danse Macabre*, Enervation*
11: Create Undead*
13: Finger of Death
15: Horrid Wilting*
* indicates the spell can be upcast - which is important for thre 6th level ability.
You gain a bonus homebrew cantrip that deals 1d6 necrotic damage, inflicts a critical hit on incapacitated targets, and gives the caster temp hp equal to half the damage done by the spell if the target dies from the hit (limited by max hp of the target). This cantrip is only avaiable to PCs with this subclass (so a bard can't take it, etc...).
Additionally, you are proficienct with a Scythe (heavy, d6, versatile for d8, two handed, slashing) and may use it as a weapon when casting Shilellagh.
Further, whenever you cast find familiar, you gain an undead familiar with the attributes of a normal animal familiar except the type is undead and it gains one of three abilities: Flight with a 30' speed, Blindsight 10', or Gaseous form (as the spell) once per LR for 1 minute. It is visibly undead and horrific.
Finally, you may communicate telepathically with any undead you control or create with a druid class feature, and you gain the Warlock Invocation Gaze of Two Minds, but it works on undead instead of humanoids.
6th level: When you cast any of the 13 bonus spells granted by the subclass, treat the spell as if you used a spell slot 1 levels higher. If you actually use a higher spell slot to cast the spell, double the increase in effective spell level for using the higher slot. For example, animate dead with a 3rd level slot is cast as if a 4th level spell slot was used. If a 4th level slot is used, the increase of 1 level results in 2 additional bonus levels for an effective level of 6th. If animate dead is cast using a 9th level spell slot, the effective spell level is 16th for 27 skeletons/zombies. A 9th level Shadow Veil (a 1st level spell) has an effective spell level of 18th and covers a radius of 440 feet.
Additionally, you can summon a shadow scythe as an action. It deals necrotic instead of slashing, is treated as a magical weapon, and if you hit with the attack you may use a bonus action to steal the shadow of a target that was in bright light when hit. The shadow becomes a shadow (as phb) under your control for 10 minutes, until you create another shadow, or until the target creature dies (whichever comes first).
You also treat magical darkness as if the magical darkness was bright light (at any distance). All magical darknes treated as bright light effectively creates dim light for you around it in twice the radius of the magical darkness. Other creatures, including your undead, do not benefit from this vision.
10th level: You can cast the find greater steed using spell slots, but the steed has an undead type, gains blindsight 10 feet, deals extra necorotic damage equal to your proficiency modifier when it hits with an attack, and regenerates 1 hp per minute if it has 1 hp or more.
Additionally, as an action, you may take control of large numbers of undead. Target all uncontrolled undead creatures you can see within 60 feet of you. The targets must make a Wisdom saving throw. On a failed save, the targets must obey your commands for the next 24 hours, or until you uses this ability again. An undead whose challenge rating is equal to or greater than the druid’s class level is immune to this effect. Any abilities that impacts the saving throw for a turn ability also impact this saving throw.
Further, You lose your normal type and instead become undead.
14th level: You may travel to the Shadowfell from any plane, or from the Shadowfell to the prime material plane. Both require only an action. You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
