Warlock of Strahd

Grave Touched.  Once during each of its turns, when it hits a creature with an attack roll and rolls damage against the creature, the warlock can replace the damage type with necrotic damage and roll one additional damage die when determining the necrotic damage the target takes.

Regeneration. The warlock 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 warlock's next turn.

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

Vampire Weaknesses. The warlock has the following flaws:

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

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

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

Sunlight Hypersensitivity. The warlock takes 20 radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

Spellcasting. The warlock is a 11th level spell castser, using Charisma as the spellcasting ability (spell save DC 15):

At will: detect magic, eldritch blast, levitate, mage armor (self only), mage hand, minor illusion, prestidigitation, shocking grasp, speak with dead

1/day each: arcane gate,  fog cloud, negative energy flood

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one willing creature, or a creature that is grappled by the warlock, 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 warlock 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.

Charm. The warlock targets one humanoid he can see within 30 feet. If the target can see warlock the target must succeed on a DC 15 Wisdom saving throw against this magic or be charmed. The charmed target regards the warlock as a trusted friend to be heeded and protected. The target isn’t under the warlock's control, but it takes the warlock's requests and actions in the most favorable way and lets the warlock bite it.

Each time the warlock or it'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 1 hour or until the warlock is destroyed, is on a different plane of existence than the target, or takes a bonus action to end the effect.