Auril's Black Knight Commander

Chilling Aura. Whenever a creature starts its turn within 10 feet of the black knight or hits it with a melee attack while within 5 feet of it, that creature takes 10 (3d6) cold damage.

Dark Advantage. Once per turn, the black knight can deal an extra 10 (3d6) damage when they hit with a weapon attack, provided it has advantage on the attack roll.

Dark Devotion. The black knight has advantage on saving throws against being charmed or frightened.

Dark Weapons. The black knight's weapon attacks are considered magical. When it hits with any weapon, the attack deals an extra 7 (2d6) necrotic damage.

Disheartening Strike (4/Day). When the black knight hits a creature with its greatsword, it can fill the target with unsettling dread: the target has disadvantage on the next saving throw it makes before the end of the black knight's next turn.

Fearmonger. The black knight has advantage on attack rolls against any creature that is frightened of it.

Marshal Undead. Unless the black knight is incapacitated, it and undead creatures of its choice within 60 feet of it have advantage on saving throws against features that turn undead.

Special Equipment. The black knight wields an Acheron Blade Greatsword. 

Spellcasting. The black knight is a 8th level spellcaster. Its spellcasting ability is Charisma (spell save DC 17, +9 to hit with spell attacks). The black knight has the following spells prepared:
Cantrips (at will): chill touch, ray of frost, thaumaturgy, toll the dead
1st level (4 slots): cause fear, frost fingers, inflict wounds, shield of faith
2nd level (3 slots): blindness/deafness, hold person, spiritual weapon
3rd level (3 slots): fear, phantom steed, spirit shroud
4th level (2 slots): ice storm, shadow of moil

Multiattack. The black knight makes two greatsword attacks. 

Acheron Blade Greatsword. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage plus 7 (2d6) necrotic damage.

Dark Command. The black knight targets one ally it can see within 30 feet of it. If the target can see and hear the black knight, the target can make one weapon attack as a reaction, gains advantage on the attack roll, and the attack deals an extra 7 (2d6) necrotic damage if it hits.

Dark Blessing (4/Day). The black knight raises its greatsword into the air gaining 1d4+4 temporary hit points.

Chilling Parry. The black knight adds 4 to its AC against one melee attack that would hit it. To do so, the death knight must see the attacker and be wielding a melee weapon. If the attack is successfully deflected, the attacker takes 7 (2d6) cold damage and has its speed reduced by 10 feet until the end of their next turn.