The Circle of Bones! Get your bone on. Wait. No. Don't do that.
To be honest, I didn't think this was the direction this subclass would go — I don't normally like basing designs around specific spells. But it became pretty clear that reanimation was the answer to all the things the subclass needed to do.
First, a quick overview of the differences between reanimation and animate dead. Reanimation is the Spells That Don't Suck version. The big difference is that instead of straightforwardly creating skeletons and zombies, it takes the existing stat block of your target and applies a template to it, turning it into an undead creature. A small-but-significant difference is that there's a combined CR limit for all the undead you command. With basic animate dead, that limit doesn't exist; if you cast the spell multiple times (for instance, if something lets you cast it on a short-rest recharge), then you can potentially amass quite the horde. The CR limit means that even if you cast reanimation several times a day, you still won't get a wild amount of minions.
The Features
Okay, with the preamble out of the way, let's talk about the subclass! Your Spell List is heavily skewed towards necromancy — almost entirely homebrew spells written to accompany the necromancer class. I considered putting some more conventional druid stuff in here, to help accomplish the blending-of-the-two flavor, but that's what your regular spell selection is for. Rotten Wilds is your core feature. Instead of using your Wild Shape, you can cast reanimation. (Note that it doesn't actually add regular reanimation to your spell list; you can only cast it by spending your Wild Shape). It only animates beasts, and it can scale down to function like a 2nd-level spell. At level 6, you get Natural Undeath, which lets you grant your minions cool extra features (vines, bark, or bugs). Level 10 brings you Death's Harvest, letting you create temporary hit points from creatures on death. And Level 14 adds Life From Death, which lets you cast druid spells over your minions as they expire. At this point, it's a real struggle to make minions scale — so you can stop bothering and start using them as spell bombs instead!
As always, you're invited to come discuss and offer feedback on Discord! This sub will almost certainly get included in Machines of Bone and Blood — it's too thematically on-point not to.
Art: Nikya of the Old Ways, by Ryan Pancoast © Wizards of the Coast LLC