Vampyr

Regeneration. Vampyr regains 20 hit points plus 10 per creature connected by Blood Syphon at the start of each of its turns.

Contaminated Blood. At the start of each of its turns Vampyr emits a eruption of corrupt blood 30 feet in every direction, coating the ground and any creature in range, making the ground into difficult terrain. Any creature that starts its turn within that 30ft range must succeed on a DC 20 Constitution saving throw or take 14 (4d6) Necrotic damage. A creature that succeeds on the save is resistant to the effects of the Contaminated Blood and Gout of Blood for the next 24 hours. 

Innate Spellcasting. Vampyr's innate spellcasting ability is Charisma (spell save DC 21). It can innately cast the following spells, requiring no material components:

At will: charm person, command, dispel magic, hold monster.

Legendary Resistance (3/Day). If the Vampyr fails a saving throw, it can choose to succeed instead.

Multiattack. Vampyr makes 4 attacks, only one of which may be a Bite attack. The other three attacks may be any combination of its Slam or Blood Syphon attacks.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 9 (2d8) piercing damage plus 13 (3d8) Necrotic damage. The target’s hit point maximum is reduced by an amount equal to the necrotic damage taken, and Vampyr regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if its hit point maximum is reduced to 0. A humanoid slain in this way is transformed into a vampire spawn under Vampyr's control. The transformation can only be undone by a wish spell.

Slam. Melee Weapon Attack: +9 to hit, reach 20 ft., one target. Hit: 20 (3d12) bludgeoning damage.

Blood Syphon. Ranged Weapon Attack: +9 to hit, range 60 ft., one target that must be below hit point maximum and have no temporary hit points. Hit: 18 (2d6 + 9) piercing damage plus 12 (3d8) necrotic damage. The target must make a DC 20 Constitution saving throw. On a failure, a fleshy tendril of congealed blood forms, connecting the target to Vampyr. A tendrilled target cannot move further than 80 feet away from Vampyr. A target can only be affected by a single tendril at a time. The tendril has an AC of 10, 18 HP, and the same damage resistances and vulnerabilities as Vampyr. A creature can use its action to attempt a Strength (Athletics) check against DC 20 to pull a tendril free, dealing 15 (5d6) piercing damage to the tendrilled target on a success.

Sever. Vampyr rips all tendrils free of their hosts. Each tendrilled creature takes 15(5d6) piercing damage must make a DC 20 Strength or Dexterity saving throw or be knocked prone.

Oppressive Will (3/Day). Vampyr targets up to three creatures it can see within 90 feet of it. Each target must make a DC 20 Constitution saving throw. On a successful save, a creature becomes immune to Oppressive Will. On a failed save, the target gains 1 level of exhaustion. While suffering ]exhaustion in this way, the target must repeat the saving throw at the start of each of its turns. Three successful saves against the effect ends it, and removes any levels of exhaustion. Each failed save causes the target to suffer another level of exhaustion. Once the target reaches 6 levels of exhaustion, it dies and instantly transforms into a vampire spawn under Vampyr's control. The transformation can only be undone by a wish spell.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 9 (2d8) piercing damage plus 13 (3d8) Necrotic damage. Vampyr may make use its reaction to bite any creature within 10 feet of it. The target’s hit point maximum is reduced by an amount equal to the necrotic damage taken, and Vampyr regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if its hit point maximum is reduced to 0. A humanoid slain in this way is transformed into a vampire spawn under Vampyr's control. The transformation can only be undone by a wish spell.

Vampyr can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Vampyr regains spent legendary actions at the start of its turn.

Sever. (Costs 2 Actions) Vampyr uses Sever.

Gout of Blood. Vampyr targets one creature it can see within 90 feet of it. The target must succeed on a DC 20 Dexterity saving throw or take 30 (9d6) (half on a successful save) necrotic damage as it is coated in corrupted blood.

Oppressive Will (Costs 2 Actions). Vampyr uses Oppressive Will.