Vampyr

Shapechanger. If Vampyr isn't in sunlight, it can use its action to polymorph into its bat form, a cloud of mist, or back into its true form.

• Crowned Beast. Vampyr's bat form is monstrous, with a shadowy crown that floats above its head, slowly rotating. While in bat form, Vampyr's walking speed is 10 feet, it has a flying speed of 60 feet, and its bite attack does an extra 2d10 piercing damage.  Its statistics, other than its speed, are unchanged. It reverts to its true form if it dies.
• Mistborn. While in mist form, Vampyr has a flying speed of 20 feet, can hover, and can enter a hostile creature's space and stop there. If a creature starts its turn while in the same space as Vampyr, it takes 2d12 necrotic damage, and Vampyr regains that amount of hit points. 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 nonmagical damage, except the damage it takes from sunlight.

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

Shadow Stride. Vampyr can use a bonus action to step from one shadow into another. When in dim light or darkness, Vampyr can teleport up to 60 feet to an unoccupied space it can see that is also in dim light or darkness.

Blood Bond. If Vampyr has used the Gather Blood legendary action, it can move the blood sphere up to 60 feet as a bonus action.

Regeneration. Vampyr regains 170 hit points at the start of its turn if it has at least 1 hit point and isn't in sunlight. If Vampyr takes radiant damage, this trait doesn't function at the start of the Vampyr's next turn.

Vampire Weaknesses. Vampyr has the following flaws:
Sunlight Hypersensitivity. Vampyr takes 50 radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

Multiattack. (True Form Only). Vampyr makes two attacks, only one of which can be a bite attack.

Unarmed Strike (True Form Only). Melee Weapon Attack: +18 to hit, reach 10 ft., one creature. Hit: 30 (4d10 + 9) bludgeoning damage. Instead of dealing damage, Vampyr can grapple the target (escape DC 23).

Bite. (Bat or True Form Only). Melee Weapon Attack: +18 to hit, reach 5 ft., one creature affected by Charm of the Ancients, or a creature that is grappled by Vampyr, incapacitated, or restrained. Hit: 35 (5d10 +9) piercing damage plus 100 necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and Vampyr 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 Vampyr's control.

Vampyr can also use its bite attack to swallow the blood sphere created by Gather Blood, gaining the amount of hit points held by the blood sphere. Once swallowed, the blood sphere disappears.

Charm of the Ancients.  If any creature is within 60 ft. of Vampyr, they must succeed on a DC 17 Wisdom saving throw against this magic or be mesmerized by Vampyr, as if under the sympathy effect of the Antipathy/Sympathy spell, as follows:

• Sympathy. The enchantment causes the specified creatures to feel an intense urge to approach Vampyr while within 60 feet of it or able to see it. If a creature fails its saving throw, it must use its movement on each of its turns to enter the area or move within reach of Vampyr. When the creature has done so, it can't willingly move away from Vampyr. If Vampyr damages or otherwise harms an affected creature, the affected creature can make a Wisdom saving throw to end the effect, as described below.

• Ending the Effect. If an affected creature ends its turn while not within 60 feet of Vampyr or able to see it, the creature makes a Wisdom saving throw. On a successful save, the creature is no longer affected by Vampyr and recognizes the feeling of repugnance or attraction as magical. In addition, a creature affected by Vampyr is allowed another Wisdom saving throw every 24 hours until it is destroyed, or is on a different plane of existence. A creature that successfully saves against this effect is immune to it for 1 minute, after which time it can be affected again.

Night's Children (1/Day). Vampyr magically calls 2d4 swarms of shadowy bats or rats (swarm of bats, swarm of rats), or 1d4 shadows (shadow), provided that the sun isn't up. While outdoors, Vampyr can call 3d6 dire wolves (dire wolf) instead. The called creatures arrive in 1d4 rounds, acting as allies to Vampyr and obeying its commands. The beasts remain for 1 hour, or until Vampyr dismisses them as a bonus action.

Vampyr 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. Vampyr regains spent legendary actions at the start of its turn.

Move. Vampyr moves up to its speed without provoking opportunity attacks.

Bite. (Costs 2 Actions). Vampyr makes one bite attack.

Gather Blood. (Costs 3 Actions). Vampyr pulls blood from the pores of creatures affected by Charm of the Ancients into a blood sphere (AC 12) that is 5 feet in diameter. Each creature affected takes 2d12 necrotic damage. The affected creature's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the blood sphere gains hit points equal to that amount. The reduction lasts until the affected creature finishes a long rest. The affected creature dies if this effect reduces its hit point maximum to 0.