Vulpes au Uel, "The Relentless"

Gold Sight. Magical darkness doesn’t impede Vulpes darkvision.

Legendary Resistance (3/Day, or 4/Day in Lair). If Vulpes fails a saving throw, it can choose to succeed instead.

Shadow Escape. If Vulpes drops to 0 Hit Points outside its resting place, it teleports into its resting place unless it is in running water or sunlight. If it can’t teleport, it is destroyed. Once inside its resting place, it has the Paralyzed condition for 1 hour, after which it regains 1 Hit Point.

Magic Resistance. Vulpes has advantage on saving throws against spells and other magical effects.

Regeneration. Vulpes regains 20 hit points at the start of his turn. If he takes radiant damage, this trait doesn’t function at the start of his next turn. Vulpes dies only if he starts his turn with 0 hit points and doesn’t regenerate.

Multiattack. Vulpes makes three attacks, using Grave Strike or Sickening Ray in any combination.

Grave Strike. Melee Attack Roll: +16, reach 5 ft. Hit: 17 (2d8 + 8) Slashing damage plus 36 (8d8) Necrotic damage.

Sickening Ray. Ranged Attack Roll: +16, range 120 ft. Hit: 16 (2d10 + 8) Necrotic damage, and the target has the Poisoned condition until the start of the vampire’s next turn.

Hunger of Hadar (Recharge 5–6). Vulpes casts Hunger of Hadar (level 7 version), requiring no spell components and using Charisma as the spellcasting ability (spell save DC 26).

Spellcasting. Vulpes casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 26):

At will: alter self (can become Medium when changing his appearance), detect evil and good, fireball, invisibility (self only), major image

3/day each: blade barrier, dispel evil and good, finger of death, Dominate Person

1/day each: Antimagic Field

Teleport. Vulpes teleports, along with any equipment he is wearing or carrying, up to 120 feet to an unoccupied space he can see.

Sanguine Drain. Constitution Saving Throw: DC 25, one creature Vulpes can see within 30 feet that isn’t a Construct or an Undead. Failure: 18 (6d6) Necrotic damage. The target’s Hit Point maximum decreases by an amount equal to the damage taken, and Vulpes regains Hit Points equal to that amount.

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, Vulpes can expend a use to take one of the following actions. Vulpes regains all expended uses at the start of each of its turns.

Beguile. Vulpes casts Command, requiring no spell components and using Charisma as the spellcasting ability (spell save DC 26). Vulpes can’t take this action again until the start of its next turn.

Umbral Strike. Vulpes moves up to half its Speed, and it makes one Grave Strike or Sickening Ray attack.

Teleport. Vulpes uses Teleport.