Valadk the Night Warden

Shapechanger. Valadk can use its action to polymorph into a a Large cloud of mist, or back into its true form.

While in mist form, Valadk can't take any actions, speak, or manipulate objects. It is weightless, has a flying speed of 40 feet, can hover, and can enter a hostile creature's space and stop there. In addition, if air can pass through a space, the mist can do so without squeezing, and it can’t pass through water. It has advantage on Strength, Dexterity, and Constitution saving throws, and it is immune to all damage except psychic, radiant, and force.

Legendary Resistance (3/Day). If Valadk fails a saving throw, it can choose to succeed instead.

Regeneration. Valadk regains 30 hit points at the start of its turn if it has at least 1 hit point and it’s phylactery is still intact. If Valadk takes radiant damage or damage from holy water, this trait doesn't function at the start of its next turn.

Vampire Weaknesses. Valadk has the following flaws:

Forbiddance. Valadk cannot enter a building if he is not invited.

Sunlight sensitivity. Valadk has disadvantage on attack rolls and saving throws as well as wisdom (perception) checks while in direct sunlight.

Magic and Turn Resistance. Valadk has advantage against magic and magical effects as well as turn undead.

Innate Spellcasting. Valadk spellcasting modifier is intelligence (spell save DC 19, +11 to hit). Valadk can cast the following wizard spells:

at will: chill touch, disguise self, animate dead, vampiric touch, suggestion, counterspell, 

3/day each: greater invisibility, enervation, create undead, soul cage, polymorph, immolation

1/day: imprisonment, clone, wish, tether essence, dark star

Multiattack. (Vampire Form Only). The vampire makes two attacks, only one of which can be a bite attack.

Unarmed Strike (Vampire Form Only). Melee Weapon Attack: +11 to hit, reach 5 ft., one creature. Hit: 11 1d8 + 7) bludgeoning damage. Instead of dealing damage, Valadk can grapple the target (escape DC 19).

Leeching Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 16 (2d8 + 7) piercing damage plus 33 (6d10) necrotic damage, and the target must succeed on a DC 19 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and Valadk regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. A humanoid slain in this way and then buried in the ground rises the following night as a vampire spawn under its control.

Children of the Night (1/Day). Valadk magically calls 2d4 specters, wraiths, or horrors provided that the sun isn't up. While outdoors, Valadk can call 1d6 gloomstalkers instead. The called creatures arrive in 1d4 rounds, acting as allies of Valadk and obeying its spoken commands. The beasts remain for 1 hour, until Valadk dies, or until Valadk dismisses them as a bonus action.

Valadk can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. Valadk regains spent legendary actions at the start of its turn.

Move. The Valadk moves up to its speed without provoking opportunity attacks.

Strike. Valadk makes one unarmed strike or bite attack.

Spell attack (Costs 2 Actions). Valadk casts a spell.