Blood Dragon

Bleeding Body.
A creature that attacks the dragon within 5 feet of it is sprayed with a burst of blood. The target must succeed on a DC 21 Constitution saving throw or become poisoned until the end of its next turn.

Blood Drinker.
When the dragon kills a creature with a vascular system, it immediately absorbs its blood. The dragon gains 20 temporary hit points and gains advantage on its attack rolls for the next 1 minute.

Blood Form.
The dragon can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Blood Magic Immunity.
The dragon cannot be affected by spells of the blood magic subschool unless it wishes to be, and has advantage on saving throws made to resist the effects of necromancy spells.

Bloodied Grappler.
The dragon can grapple up to 10 targets, blood sloughing off from its form to wrap around these targets. For each target it is grappling beyond the first, the dragon's AC decreases by 1.

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

Multiattack.
The dragon makes one Bite attack and one Claws attack, it can make one Drain attack (if it is grappling another creature), and it can use its Frightful Presence.

Bite.
Melee Weapon Attack: +14 to hit, reach 10 ft., one target.
Hit: 18 (2d10 + 7) Piercing damage plus 5 (1d10) Necrotic damage. Tendrils of blood burst forth from the dragon's mouth. If the target is Large or smaller the dragon can grapple it. The target must succeed on a DC 22 Strength saving throw or be grappled by the dragon.

Claws.
Melee Weapon Attack: +14 to hit, reach 5 ft., one target.
Hit: 14 (2d6 + 7) Slashing damage. Tendrils of blood burst forth from the dragon's claws. If the target is Large or smaller the dragon can grapple it. The target must succeed on a DC 22 Strength saving throw or be grappled by the dragon.

Drain.
Melee Weapon Attack: +14 to hit, reach 10 ft., one target that is grappled by the dragon.
Hit: 20 (2d12 + 7) Piercing damage plus 14 (4d6) Necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the blood dragon gains temporary 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.

Tail.
Melee Weapon Attack: +14 to hit, reach 15 ft., one target.
Hit: 16 (2d8 + 7) Bludgeoning damage. Tendrils of blood drip from the dragon's tail. If the target is Large or smaller the dragon can grapple it. The target must succeed on a DC 22 Strength saving throw or be grappled by the dragon.

Bloody Breath (Recharge 5-6).
The dragon exhales clotting blood in a 60-foot cone. Each creature in that area must make a DC 21 Constitution saving throw, taking 54 (12d8) Necrotic damage on a failed save, or half as much damage on a successful one. The ground beneath the cone becomes covered in blood. A creature attempting to move across the blood covered ground must succeed on a DC 21 Dexterity saving throw, or fall prone at the end of its movement, slipping on the blood.

Frightful Presence.
Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 20 Wisdom saving throw or become frightened of the dragon for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Spellcasting.
The dragon casts one of the following spells, using Charisma as its spellcasting ability modifier (spell save DC 22):

At Will: Anemia, Hemorrhage, Seek Blood.

3/Day: Blight (At 6th level).

Bloodied Veil (Recharge 5-6).
In response to taking damage, the dragon causes portions of its bloody body to burst forth, flowing around it in a cyclone of disgusting blood which creates a 10-foot-radius sphere of magically flying blood. Each creature in the area other than the blood dragon must make a DC 21 Constitution saving throw, taking 20 (8d4) Necrotic damage on a failed save, or half as much damage on a successful one. The area is heavily obscured for creatures other than the dragon until the start of the dragon's next turn.

The dragon 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. The dragon regains spent legendary actions at the start of its turn.

Blood Contortion.
The dragon attempts to control the blood of another creature with a vascular system within 120 feet of it that it can see. The creature must succeed on a DC 20 Wisdom saving throw or be compelled to move up to 15 feet in a direction of the dragon's choice. During this movement, the creature does not avoid hazardous terrain or threatened spaces.

Tail Attack (Costs 2 Actions).
The dragon makes a Tail attack.

Wing Attack (Costs 3 Actions).
The dragon flings necrotic-infused blood from its body, unfurling disgusting wings. Each creature within 10 feet of the dragon must succeed on a DC 22 Dexterity saving throw or take 14 (2d6 + 7) Necrotic damage and become poisoned until the start of the dragon's next turn. The dragon can then fly up to half its flying speed.