Shattered Circle

You have broken the trust of those in your circle, becoming an outcast and beginning to study "unethical" magics

Reanimated Wild Shape

When you choose this circle at 2nd level, you lose your connection to nature, including your ability to transform into animals. However, the dark magics you practice allow you to turn into Undead instead

Circle Forms

Your past transgressions against your circle allow you to transform into Undead instead of beasts with a CR equal to or lower than 1 (you ignore the Max. CR column of the Undead Shapes table, but must abide by the other limitations there).

Starting at 6th level, you can transform into a Undead with a challenge rating as high as your druid level divided by 3, rounded down.

Undead Servant

Once per long rest, you can create a Skeleton that can use any items and armor you give it, it can understand your commands and has a bonus to it's hitpoints equal to your wisdom modifier, you can create it anywhere you can see within 30ft.

Corrupt the Earth

Starting at 6th level, as an action while standing on a natural surface (Grass, Rocks, Water, ETC) You can strike the ground with your fist, causing a 20x20 ft circle around you to rot, corrode, and decay, this makes it:

-Become difficult terrain (Besides for you)

-Any creature besides You, Undead, Fiends, and Monstrosities, must make a DC 10 + Your Wisdom modifier dexterity saving throw, otherwise they become entangles and take 1d4 + your Druid Level halved rounded up necrotic damage, you heal any necrotic damage dealt by this, if you are at max hitpoints, you gain half the damage dealt by this as temporary hitpoints

Corrupt the Earth affects the surface for 1d4 hours or until you die. 

Tainted Blows

The rites of your circle grant you the ability to transform into more dangerous forms. Starting at 6th level, you can transform into an undead with a challenge rating as high as your Druid Level divided by 3 rounded down. any attacks you throw now deal half your Druid Level rounded up as necrotic damage whenever you hit (regardless if you use a weapon or not)

Slay the Natural

At the 10th level, you have an advantage on attack rolls against Plants, Beasts, and creatures with at least 1 level in druid, ranger, or Oath of the Ancients paladin. An equal amount of times as your proficiency bonus that refreshes after a long rest, you can also deal crit damage to one of these creatures after hitting them.

Scorn of Nature

By 14th level, you have become popular with the entities that nature has also exiled, be it demons or evil gods, they are rooting for you, giving you:

-The Undead Fortitude trait once per long rest when not wild shaped into Undead.

-The ability to Wild shape into Fiends

-Once per long rest, you can summon a 10ft radius of fear around you, any creature must make a DC 10 + Your wisdom modifier or become frightened for 1d4 minutes or until attacked, this lasts for 1d10 minutes or until you dismiss it.

-An extra D10 radius damage to your Corrupt the Earth Ability

-The ability to automatically raise the corpse of any Beast or Plant that you kill using a melee weapon, their creature type becomes undead, and they die after 3 rounds or when combat ends, they have the initiative roll they had before dying, you can use this feature an equal amount of times to your proficiency bonus, this refreshes after a long rest