Misty Escape. When the vampyre has been reduced to 0 hitpoints, it falls to 1 hitpoint instead. It turns into a cloud of mist, which can move at a rate of 30 ft per round (flying). This cloud is immune to all damage and conditions. It will return to its coffin in Darkmeyer, where it will re-coalesce into physical form and receive the incapacitated condition for 1 hour. After that, it will regain all of its hitpoints.

If it is attacked while in his coffin and damaged, it will be permanently slain.

Its misty escape ability will be negated if it has been hit by a Guthix Balance potion within the past minute. In this case, if it drops to 0 hitpoints, it will simply die.

Holy Vulnerability. If the vampyre is splashed by a Guthix Balance Potion, its Misty Escape ability will be deactivated for the next minute, although it will take no damage from the potion.

Unholy Invulnerability. The vampyre is completely immune to all damage that is not dealt by a weapon specifically made to kill vampyres. Additionally, it cannot be forcefully inflicted with any condition by spells that are not cast using a spellcasting focus that is made to kill vampyres. It CAN be effected by spells that manipulate the environment around it (such as Grease or Fog Cloud), but any spell that targets it directly (such as Grasping Vine or Hold Monster) fails unless the vampyre chooses to allow itself to be affected by it. It also can be subjected to conditions by physical means; for example, throwing a net over it may restrain it, and blindfolding it may blind it. 

Sunlight Vulnerability. While in direct sunlight, the vampyre has disadvantage on all attacks and ability checks.

Shapechanger. The vampyre has two forms, which it can switch between at will using an action. Its first form, its human form, can pass for being human in most circumstances as it is distinguishable from human only by its pale pallor and its fangs (which are hidden when the mouth is closed).

Its second form, its true form, looks like some sort of hybrid between a bat and a human, with a roughly human shape but a bat-like face and large wings.

Spellcaster. The vampyre is an 8th level spellcaster. Its spell stat is Charisma. Its spell attack bonus is +8 and its spell save DC is 16. It has the following sorcerer spells prepared.

Cantrips: Friends, Mind Sliver, Chill Touch, Mage Hand, Message

First Level Spells (4 slots): Ray of Sickness, Fog Cloud, Charm Person, Detect Magic

Second Level Spells (3 slots): Darkness, Detect Thoughts, Misty Step, Hold Person

Third Level Spells (3 slots): Vampyric Touch, Fear, Hypnotic Pattern

Fourth Level Spells (4 slots): Blight, Dimension Door, Vitriolic Sphere

Multiattack. When the vampyre takes the attack action, it can attack twice, once with its claws and once with its bite. 

Claw: Melee weapon attack. Range of 5 ft, 1 target. + 9 to hit, deals 9 (1d8 + 4) slashing damage.

Bite: Melee weapon attack. Range of 5ft, 1 target. + 9 to hit, deals 8 (1d6 + 4) piercing damage plus 7 (2d6) necrotic damage. The vampyre regains hitpoints equal to the amount of necrotic damage it dealt. Additionally, each time a target is hit by the bite attack, it must succeed a DC 14 constitution saving throw or take one level of exhaustion due to blood loss.

Spellcaster. The vampyre casts a spell that requires an action to cast.