Shapechanger. If is not in sunlight, it can use its action to polymorph into a Giant bat, Dire wolf, a Large cloud of mist, or back into its true form.

While in Giant bat form, the avatar uses move speed from form, all other attributes stay the same. Anything it is wearing transforms with it, but nothing it is carrying does. It reverts to its true form if it dies.

While in vampiric mist form, the vampire can't take any actions, speak, or manipulate objects. It is weightless, has a flying speed of 30 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 same advantages as true form on saving throws and damage.

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

Misty Escape. When it drops to 0 hit points outside its resting place, the vampire transforms into a cloud of mist provided that it isn't in sunlight. If it can't transform, it is destroyed.

While it has 0 hit points in mist form, it can't revert to its vampire form, and it must reach its resting place within 2 hours or be destroyed. Once in its resting place, it reverts to its vampire form. It is then paralyzed until it regains at least 1 hit point. After spending 1 hour in its resting place with 0 hit points, it regains 1 hit point.

Regeneration. The vampire regains 25 hit points at the start of its turn if it has at least 1 hit point and isn't in sunlight. If the vampire takes radiant damage or damage from holy water, this trait doesn't function at the start of the vampire's next turn.

Spider Climb. The vampire can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Spellcasting. The vampire is a 13th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 16, +8 to hit with spell attacks). The vampire has the following wizard spells prepared:

Cantrips (at will):  chill touch, friends, mind sliver, toll the dead, true strike 

1st level (4 slots): cause fear, disguise self, false life, ray of sickness

2nd level (3 slots): blindness/deafness, mind thrust, ray of enfeeblement

3rd level (3 slots):  counterspell, nondetection, tongues

4th level (3 slots): blight, dimension door, ice storm

5th level (2 slot): geas, negative energy flood

6th level (1 slot): freezing sphere

7th level (1 slot): plane shift

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

Unarmed Strike (Vampire Form Only). Melee Weapon Attack: +10 to hit, reach 5 ft., one creature. Hit: 11 (1d10 + 5) bludgeoning damage. Instead of dealing damage, the vampire can grapple the target (escape DC 20).

Bite. (Bat, Wolf, or Vampire Form Only). Melee Weapon Attack: +10 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the vampire, incapacitated, or restrained. Hit: 9 (1d8 + 4) piercing damage plus 14 (3d8) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the vampire 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 the vampire's control.

Life Drain. (Mist Form Only) The mist touches one creature in its space. The target must succeed on a DC 13 Constitution saving throw (undead and constructs automatically succeed), or it takes 10 (2d6 + 3) necrotic damage, the mist regains 10 hit points, and the target’s hit point maximum is reduced by an amount equal to the necrotic damage taken. This reduction lasts until the target finishes a long rest. The target dies if its hit point maximum is reduced to 0.

Charm. The vampire targets one humanoid it can see within 30 feet of it. If the target can see the vampire, the target must succeed on a DC 19 Wisdom saving throw against this magic or be charmed by the vampire. The charmed target regards the vampire as a trusted friend to be heeded and protected. Although the target isn't under the vampire's control, it takes the vampire's requests or actions in the most favorable way it can, and it is a willing target for the vampire's bite attack.

Each time the vampire or the vampire's companions do anything harmful to the target, it can repeat the saving throw, ending the effect on itself on a success. Otherwise, the effect lasts 24 hours or until the vampire is destroyed, is on a different plane of existence than the target, or takes a bonus action to end the effect.

Children of the Night (1/Day). The vampire magically calls 3d4 swarms of bats or rats (swarm of bats], swarm of rats), provided that the sun isn't up. While outdoors, the vampire can call 4d6 wolves (wolf) instead. The called creatures arrive in 1d4 rounds, acting as allies of the vampire and obeying its spoken commands. The beasts remain for 1 hour, until the vampire dies, or until the vampire dismisses them as a bonus action.

The vampire 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. The vampire regains spent legendary actions at the start of its turn.

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

Unarmed Strike. The vampire makes two unarmed strike.

Bite. The vampire makes one bite attack.