Deathbringer

At 3rd level, you can channel a fragment of your patron’s necromantic power.  While you're raging, you have resistance to necrotic damage and the first creature you hit on each of your turns with a weapon attack takes extra necrotic damage equal to 1d4 + half your Barbarian level.

Coldblooded Killer

Beginning at 6th level, you can't be charmed or frightened while raging. If you are charmed or frightened when you enter your rage, the effect is suspended for the duration of the rage.

Half-Dead

Starting at 10th level, you become increasingly more like an undead creature.  You are immune to poison and disease.  You need to eat and drink only 1/4 as much as a living creature and can hold your breath for four times as long as normal.  Your hit point maximum can't be reduced.   Particularly unintelligent undead like skeletons and zombies look at you as one of their own, unless they are directly ordered to attack you or unless you attack them.

Raise the Fallen

At 14th level, you gain some of your master’s ability to animate the dead. As a bonus action, you can choose a pile of bones or a corpse of a Medium or Small humanoid within 10 feet.  It raises as a skeleton or zombie.  It obeys all your commands until it is destroyed or until you dismiss it as a bonus action.  You can use this feature a number of times equal to your Constitution modifier (minimum 1).  You regain any expended uses when you finish a long rest.

You can have up to 3 undead under your control at a time.

You are encouraged to replace the 20th level feature Primal Champion with the following ability:

Conjure Wand of Orcus

By 20th level, even the Demon Prince of the Undead is impressed at the trail of corpses you have left behind.  He will lend you his dreaded Wand for brief periods, confident that you will put it to good use.  You can spend an action to summon the Wand of Orcus for 1 minute.  Normally, it is around 10 feet long, but Orcus helpfully shrinks it to a more appropriate size.

The Wand of Orcus is a +3 greatclub that deals an additional 2d12 necrotic damage.  You cannot use the Wand as effectively as Orcus can, but you still gain access to much of its fell might.

The wand has 7 charges, and any of its properties that require a saving throw have a save DC of 18.  You  can expend 1 or more of the wand's charges to cast one of the following spells from it : Animate Dead (1 Charge), Blight (1 Charge), Circle of Death (2 Charges), Finger of Death (2 Charges) or Speak with Dead (1 Charge).  You can cast these spells while raging.

While holding the wand, you can use an action to conjure undead creatures whose combined average hit points don't exceed 75. These undead magically rise up from the ground or otherwise form in unoccupied spaces within 300 feet of you and obey your commands until they are destroyed, you dismiss them as an action, or until the next time you use this property. This property of the wand can be used only once each time you possess it.

Once you use this feature, you can’t use it again until you finish a long rest.