Ctenmiir the Vampire

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

When it drops to 0 hit points outside its resting place, Ctenmiir 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.

Ctenmiir 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 Ctenmiir takes Radiant damage or damage from holy water, this trait doesn't function at the start of Ctenmiir's next turn.

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

Ctenmiir has the following flaws:
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Forbiddance
Ctenmiir can't enter a residence without an invitation from one of the occupants.
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Harmed by Running Water
Ctenmiir 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 Ctenmiir's heart while Ctenmiir is Incapacitated in its resting place, Ctenmiir is Paralyzed until the stake is removed.
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Sunlight Hypersensitivity
Ctenmiir takes 20 Radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

Ctenmiir 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, Ctenmiir 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 Ctenmiir, 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 Ctenmiir 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 Ctenmiir's control.

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

Ctenmiir magically calls 2d4 swarms of Bats or Rats, provided that the sun isn't up. While outdoors, Ctenmiir can call 3d6 Wolves instead. The called creatures arrive in 1d4 rounds, acting as allies of Ctenmiir and obeying its spoken commands. The beasts remain for 1 hour, until Ctenmiir dies, or until Ctenmiir dismisses them as a bonus action.

Ctenmiir moves up to its speed without provoking opportunity attacks.

Ctenmiir makes one unarmed strike.

Ctenmiir makes one bite attack.