Ok, so this is loosely based on the 3.5 Zombie Lord abilities so take a look and tell me what you guys think, I have no idea where to place the CR/XP for this thing and I am not at all opposed to lowering the HP/HD as it will not be a solo creature in the fight:
Zombie Lord
Medium undead, neutral evil
Armor Class 11
Hit Points 45 (6d8 + 18)
Speed 30 ft.
STR 13 (+1)
DEX 12 (+1)
CON 16 (+3)
INT 12 (+1)
WIS 10 (+0)
CHA 10 (+0)
Saving Throws Wis +3
Damage Immunities poison
Condition Immunities poisoned
Senses darkvision 60 ft., passive Perception 10
Languages understands the languages it knew in life
Challenge 2 (450 XP)
Aura of Death. The first round a living creature comes within 90 ft. of the Zombie Lord they must make a Constitution save DC 13 or be Poisoned. Each round the victim can make a new save, once the save is made, it cannot be affected by this aura again in the encounter.
Awaken the Dead. Once per long rest, the Zombie Lord can animate 1d6+1 Zombies if the corpses are available.
Speak With Dead. The Zombie Lord can use the Speak With Dead spell at will without needing any somatic or material components
Undead Fortitude. If damage reduces the zombie lord to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie lord drops to 1 hit point instead.
Zombie Master. The Zombie Lord can mentally command all zombies within sight at will as a free action. It can also use the senses of any zombie within a mile radius of its location as if it were standing in their place.
Actions
Multiattack. The Zombie Lord makes two slam attacks.
Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage.
The zombie lord is a living creature that has taken on the foul powers and abilities of the undead. They are formed on rare occasions as the result of a raise dead spell gone horribly wrong when cast while in the demiplane of Ravenloft.
Zombie lords look as they did in life, save that their skin has turned the pale grey of death, and their flesh has begun to rot and decay. The odor of vile corruption and rotting meat hangs about them and carrion-feeding insects often buzz about them to dine on the bits of flesh and ichor that drop from their bodies.
I have updated the Zombie Lord to reflect feedback. The following two abilities were suggested by Jadrax to fill out a signature ability from the creature:
Zombify (Recharge 5–6). The zombie lord targets one creature it can see within 30 feet of it. If the target can see the zombie lord, it must succeed on a DC 10 Constitution saving throw against this magic or become Poisoned. While the creature retains the Poisoned condition, at the end of each of the target’s turns, it must make a DC 10 Constitution saving throw. After failing three of these saving throws, the target is slain and rises as a zombie under the zombie lord's control in 1d4 rounds, and the creature is no longer Poisoned. After succeeding on three of these saving throws, the creature recovers from the Poisoned condition, and the curse ends.
Note: Just add Zombify to its list of abilities and run the creature
OR
Aura of Death. Whenever a living creature comes within 30 ft. of the zombie lord, it must succeed on a DC 10 Constitution saving throw against this magic or become Poisoned. While the creature retains the Poisoned condition, at the end of each of the creature’s turns, it must make a DC 10 Constitution saving throw. After failing three of these saving throws, the creature is slain and rises as a zombie under the zombie lord's control in 1d4 rounds, and the creature is no longer Poisoned. After succeeding on three of these saving throws, the creature recovers from the Poisoned condition, and the creature cannot be affected by this aura again in the next 24 hours.
Note: Replace the version of Aura of Death in the statblock with the above.