I came up with my own subclass. I modeled it slightly after the Circle of the Moon, which is why I'm specifically asking for comparison to it. Well, here it is.
Druid Circle: Circle of Shadows
Once there was a dark elf, he had had his heart set on joining a druid circle. All of those circles shunned him. He started his own circle. The circle of shadows.
“The shadow didn’t consume me; I consumed the shadow.”
Starting at 2nd level, when you use wild shape, you can transform into a Shadow. You also learn the Umbraturgy cantrip (from Dark Arts Players Compaion, which is homebrew). Finally, you gain darkvision for 60ft, if you already had it, it increases by 60ft.
Shadow Enhanced Strikes
“The shadow moves with me; we are becoming one.”
Starting at 6th level, your attacks in regular form and beast from are considered magical for the purpose of overcoming resistance and immunity, in addition, you can spend a spell slot and enhance a weapon. The weapon you enhanced does an extra 1d4 necrotic damage on a hit per level of expanded spell slot. You lose the effect if you leave the darkness or dimness.
Improved Shadow Form
“The shadow climbs into my soul, second by second it reaches more.”
At 14th level, when you use wild shape, you can transom into a wraith. You gain the benefits of shadow enhanced strikes while in this form.
A True Wraith
“I join hands with my shadow we sing songs of praise to the darkness that is inside me. and the darkness the he is made of. I am one with the shadow.”
At 14th level, you now can expand a spell slot to gain a hovering speed but can hover no more than 5ft off the ground. The hovering speed equals the level of the spell slot spend times 10 (1st level = 10ft 2nd level = 20ft etc.) In addition, you can cast the invisibility spell (lowest level) at will, but you must be in dim light or darkness.
Casting time: 1 action
Duration: Concentration, up to 1 hour
You compell shadows to create one of the following effects at a point you can see within range:
The shadow of a creature or object changes size or shape, up to a maximum of double or half its normal size.
You cause shadows to conceal a creature in dim light or darkness, giving them advantage on their next Dexterity (Stealth) check within the next minute as long as they remain in the dim light or darkness.
A creature or object's shape becomes either harder or softer, making its form either easier or harder to to discern from the shape of the shadow.
If you cast this spell multiple times, you can have no more than two of its non-instantaneous effects active at a time, and you can dismiss such an effect as an action.