Deathless Kind. Zaggreous doesn't need to breathe.

Innate Spellcasting. Zaggreous's innate spellcasting ability is Intelligence (spell save DC 14). He can innately cast the following spells, requiring no components:
At will: message
3/day each: zephyr strike, hold person, expeditious retreat
1/day each: ashardalon's stride, haste

Energy Drinkers (3/Long Rest). When Zaggreous attacks with his bite or social drain and hits a creature that isn't a Construct or an Undead, he can empower himself in one of the following ways of his choice:
-Zaggreous regains hit points equal to the damage dealt by the attack. 
-Zaggreous gains a bonus to the next ability check or attack roll he makes; the bonus equals the damage dealt by the attack.

Vampiric Weakness. The vampire has the following flaws:
Sunlight Sensitivity. While in sunlight, Zaggreous has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.
Glory of Battle. Zaggreous cannot bring himself to attack from range or use a ranged weapon, if he wishes to do so he has to succeed on a DC 16 Charisma Saving Throw or choose a different action. 
Icons of Pain. When Zaggreous is struck or comes into contact with a holy symbol, or ends his turn with a holy symbol touching him, he takes 2 (1d4) radiant damage.

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

Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 9 (2d4 + 4) slashing damage. Instead of dealing damage, the vampire can grapple the target (escape DC 14).

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 5 (1d4 + 3) piercing damage. While Zaggreous is missing half or more of his hit points, he has advantage on attack rolls he makes with this attack.

High-Caliber Revolver. Ranged Weapon Attack, Ammo (6), Misfire (1): +7 to hit, range 80/320ft., one creature. Hit: 13 (2d8 + 4) ballistic damage.

Social Drain. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 5 (1d4 + 3) psychic damage. While Zaggreous is missing half or more of his hit points, he has advantage on attack rolls he makes with this attack. Zaggreous has advantage on hiding the origin of this attack.

Mind Siphon (Recharge 5–6). Zaggreous targets a creature he can see within 30 feet of it. The target must make a DC 14 Intelligence saving throw, with disadvantage if Zaggreous has previously consumed the target's blood. On a failed save, the target takes 21 (6d6) psychic damage, and Zaggreous discerns the target's surface emotions and thoughts. On a successful save, the target takes half as much damage, and Zaggreous discerns the target's general emotional state but not its thoughts.

Active Regeneration. The vampire regains 5 hit points if it has at least 1 hit point and isn't in sunlight. If the vampire takes radiant damage, this trait can't be activated until the end of the vampire's next turn.