Vampire Servant

Regeneration. The vampire regains 10 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 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.

Vampire Weaknesses. The vampire has the following flaws:

Forbiddance. The vampire can't enter a residence without an invitation from one of the occupants.

Harmed by Running Water. The vampire takes 20 acid damage when it ends its turn in running water.

Stake to the Heart. The vampire is destroyed if a piercing weapon made of wood is driven into its heart while it is incapacitated in its resting place.

Sunlight Hypersensitivity. While in vampire mode the servant take 20 radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

When in non-vampire form the servant can be active in the day, but prefers dim light and hooded capes. It has no special abilities or attack modes while in this form. The servant must expend an action to change from one form to the other. 

These attacks are only for the servant in its vampire form.

Multiattack. The vampire makes two attacks, only one of which can be a bite attack.

Claws. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 8 (2d4 + 3) slashing damage. Instead of dealing damage, the vampire can grapple the target (escape DC 13).

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the vampire, incapacitated, or restrained. Hit: 6 (1d6 + 3) piercing damage plus 7 (2d6) 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.

In non-vampire form the servant has the weapon proficiencies and abilities it had in its previous life. These can range from simple to martial weapons, spell casting, and racial and class traits. [Clerics and paladins who were once of Good alignment must petition a new god/patron/oath to keep their class.]

Once per long rest the servant can try to charm a witness to its vampire form that they really didn't see anything.

When struck by an attack or effect that would reduce the servant to 0 hit-points it is instead reduced to 1 hp and turns into a mist to escape.