Spellcasting. The blackguard is a 10th-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): command, protection from evil and good, thunderous smite
2nd level (3 slots): branding smite, find steed
3rd level (2 slots): blinding smite, dispel magic
Master of Deceit. The Blackguard of Cyric has advantage on Deception checks and can make a deception check in place of any Stealth checks it makes
Illusion Scholar: The Blackguard has advantage on checks made to detect hidden creatures or see through illusions
Legendary Resistance (1/Day): Once per day, if the Blackguard of Cyric fails a saving throw, it may choose to succeed instead
Multiattack. The blackguard makes three attacks with its Longsword or two Necrotic Bolt attacks
Longsword. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) slashing damage, plus 5 (2d4) necrotic damage.
Necrotic Bolt. Ranged Spell Attack: +10 to hit, range 120 ft., one target. Hit: 25 (4d8 + 7) necrotic damage.
Dreadful Aspect (Recharge 5-6). The blackguard exudes magical menace. Each enemy within 30 feet of the blackguard must succeed on a DC 18 Wisdom saving throw or be frightened for 1 minute. If a frightened target ends its turn more than 30 feet away from the blackguard, the target can repeat the saving throw, ending the effect on itself on a success.
Blackguard's Escape (1/Day): Immediately after it is hit by an attack, the Blackguard of Cyric can use its reaction to turn invisible and teleport up to 60 feet to a spot it can see. It remains invisible until the end of its next turn or until it attacks, deals damage, or forces a creature to make a saving throw.