Voidborne Knight

Magic Resistance. The voidborne knight has advantage on saving throws against spells and other magical effects.

Spellcasting. The voidborne knight is a 19th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). It has the following paladin spells prepared:

1st level (4 slots): shield of faith, compelled duel, wrathful smite

2nd level (3 slots): shadow blade, magic weapon

3rd level (3 slots): dispel magic, blinding smite, counterspell

4th level (3 slots): banishment, staggering smite

5th level (2 slots): destructive wave (necrotic), circle of power

Born of Nothing. When a voidborne creature is reduced to 0 hit points, it must make a DC 15 Charisma saving throw. On a success, it regains all of its hit points and the DC for this feature increases by 5.

Multiattack. The voidborne knight makes three longsword attacks.

Longsword. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage, or 10 (1d10 + 5) slashing damage if used with two hands, plus 18 (4d8) necrotic damage. Additionally, creatures of the knight's choice within 30 ft. of the target take 18 (4d8) cold damage. 

Voidborne Consumption (1/Day). The voidborne knight draws energy from one creature within 30 ft. of it. The target must make a Constitution saving throw DC 18. On a failure, one of its Ability Scores reduced by 1d6 and the voidborne knight recovers up to half its maximum hit points.

Step of the Void. The voidborne knight teleports to an unoccupied space within 30 ft. of it.

Parry. The voidborne knight adds 6 to its AC against one melee attack that would hit it. To do so, the voidborne knight must see the attacker and be wielding a melee weapon. If this increase causes the attack to miss, they can make one melee weapon attack against the attacker.