Graverobber

The Graverobber
Rogues are hardly the most scrupulous of sorts. So when a rare few rogues delved into the art of necromancy, not many people were surprised. Pledging their servitude to a deceased dark King of the Dead, Vallacre, they capture the souls of those they kill and offer them to Vallacre, creating shambling masses of flesh and bones with their remaining corpses.

Wrath of Vallacre
Graverobbers are followed by a shade of Vallacre from the moment they pledge their lives to him, the ghostly lord bolstering their strength with his own. At 8th level, the Graverobber gains a Phantom of Vallacre that can be summoned (or dismissed) as a Bonus action, and is maintained indefinitely while they are conscious. The Phantom cannot be attacked, and shares the Graverobber's space, having no direct actions of its own. While the Phantom is active, the Graverobber has resistance to Necrotic damage. When the Graverobber takes the Attack action with a melee weapon while the Phantom is active, after making an attack, they can follow up with a special attack as part of the same action. It uses their normal weapon's modifier, except it's damage dice is replaced by a 2d10, and they add their Intelligence modifier to the damage instead of Strength or Dexterity. This damage is simultaneously physical and necrotic, taking advantage of either type if applicable. Additionally, if the Graverobber has already used their sneak attack, and would be capable of adding it if not for this fact, they add 2d6 necrotic damage to the attack. This increases to 3d6 at level 13 and 4d6 at level 18. If the Graverobber uses Sneak Attack on the special attack, the bonus damage is cumulative, and their normal sneak attack dice are transformed into necrotic damage.

Soul Lure
The Graverobber is, as the name implies, a thief of dead flesh and soul alike. At 13th level, whenever the Graverobber reduces an enemy to 0 hit points while their Phantom is active and the necromancer chooses to kill that creature, they may infuse the fallen creature with necrotic energy. One minute later, the fallen creature rises as either a Skeleton or a Zombie under the control of the Graverobber, using the standard stats for such creatures. These undead have additional hit points equal to the Graverobber's level, and gain a bonus equal to the Graverobber's proficency bonus to their damage rolls. These undead crumble into dust when you finish a long rest, unless you sustain them with castings of Animate Dead (which treats them as any other skeletons or zombies). Additionally, if you can cast 3rd level spells, you add Animate Dead to your list of spells known.

Fear of the Slaughterer
The Phantom of Vallacre is an intimidating sight, but only Graverobbers who have unlocked a full portion of his strength can fully capitalize on this. At 18th level, when the Graverobber uses their Phantom to attack, they attack any creature within 10' if their own melee reach is shorter. They may also target two creatures with their Phantom attack, as long as both are within their reach. Finally, whenever a creature is hit by the Phantom attack, they must make a Wisdom saving throw. If they fail, they are frightened until the end of next turn and deal half damage with their attacks.