Keresta Delvingstone

If Keresta isn't in sunlight or running water, it can use its action to polymorph into a Tiny bat or a Medium cloud of mist, or back into its true form.
While in bat form, Keresta can't speak, its walking speed is 5 feet, and it has a flying speed of 30 feet. Its statistics, other than its size and speed, are unchanged. Anything it is wearing transforms with it, but nothing it is carrying does. It reverts to its true form if it dies.
While in mist form, Keresta can't take any actions, speak, or manipulate objects. It is weightless, has a flying speed of 20 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 nonmagical damage, except the damage it takes from sunlight.

If Keresta fails a saving throw, it can choose to succeed instead.

When it drops to 0 hit points outside its resting place, Keresta transforms into a cloud of mist (as in the Shapechanger trait) instead of falling Unconscious, provided that it isn't in sunlight or running water. 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.

Keresta regains 20 hit points at the start of its turn if it has at least 1 hit point and isn't in sunlight or running water. If Keresta takes Radiant damage or damage from holy water, this trait doesn't function at the start of Keresta's next turn.

Keresta can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Keresta has the following flaws:
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Forbiddance
Keresta can't enter a residence without an invitation from one of the occupants.
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Harmed by Running Water
Keresta takes 20 Acid damage if it ends its turn in running water.
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Stake to the Heart
If a piercing weapon made of wood is driven into Keresta's heart while Keresta is Incapacitated in its resting place, Keresta is Paralyzed until the stake is removed.
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Sunlight Hypersensitivity
Keresta takes 20 Radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

Keresta makes two attacks, only one of which can be a bite attack.

Melee Weapon Attack +9 to hit, reach 5 ft., one creature. 8 (1d8 + 4) Bludgeoning damage. Instead of dealing damage, Keresta can grapple the target (escape DC 18).

Melee Weapon Attack +9 to hit, reach 5 ft., one willing creature, or a creature that is Grappled by Keresta, Incapacitated, or Restrained. 7 (1d6 + 4) Piercing damage plus 10 (3d6) Necrotic damage. The target's hit point maximum is reduced by an amount equal to the Necrotic damage taken, and Keresta 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 Keresta's control.

Keresta targets one humanoid it can see within 30 feet of it. If the target can see Keresta, the target must succeed on a DC 17 Wisdom saving throw against this magic or be Charmed by Keresta. The Charmed target regards Keresta as a trusted friend to be heeded and protected. Although the target isn't under Keresta's control, it takes Keresta's requests or actions in the most favorable way it can, and it is a willing target for Keresta's bite attack.
Each time Keresta or Keresta'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 Keresta is destroyed, is on a different plane of existence than the target, or takes a bonus action to end the effect.

The vampire magically calls 2d4 swarms of Bats or Rats, provided that the sun isn't up. While outdoors, the vampire can call 3d6 Giant Centipedes 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.

Keresta moves up to its speed without provoking opportunity attacks.

Keresta makes one unarmed strike.

Keresta makes one bite attack.