Bloodwyrm

Bloodthirsty. When the dragon reduces a creature with blood to 0 hit points, it regains 11 (2d10) Hit Points. 

Blood Frenzy. The dragon has Advantage on attack rolls against any creature that does not have all of it's Hit Points. 

Crimson Gaze. The dragon can see any creature within 30 feet of them who isn't a Construct or an Undead. This sight ignores effects that obscure sight.

Legendary Resistance (2/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Multiattack. The dragon makes three attacks using Rend. It can replace one attack with a Bite or Sting attack.

Bite. Melee Attack Roll: +10, reach 5 ft. Hit: 10 (1d10 + 5) Piercing damage plus 9 (2d8) Necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the dragon 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.

Heartburster. Constitution Saving Throw: DC 18, one creature within 30 ft that is marked with the dragon's blood. Failure. 14 (4d6) Necrotic damage. Success. Half damage. Failure or Success. The creature explodes if the target is reduced to 0 Hit Points by this action, dealing 14 (4d6) Necrotic damage. 

Rend. Melee Attack Roll: +10, reach 5 ft. Hit: 12 (2d6 + 5) Slashing damage. 

Sanguine Storm (Recharge 5–6). Dexterity Saving Throw: DC 18, each creature in a 60-foot Line. Failure:  45 (10d8) Acid damage. Success: Half damage. Failure or Success. Each creature with blood targeted by the breath weapon must make a DC 18 Constitution saving throw, or be marked. While marked with the dragon's blood, the target is Poisoned and cannot regain Hit Points. The mark lasts for an hour, after which the creature is no longer Poisoned and can regain Hit Points. 

Sting. Melee Attack Roll: +10, reach 10 ft. Hit: 12 (1d8 + 5) Piercing damage. If the creature has blood they must make a DC 18 Constitution saving throw or be marked.While marked with the dragon's blood, the target is Poisoned and cannot regain Hit Points. The mark lasts for an hour, after which the creature is no longer Poisoned and can regain Hit Points. 

Legendary Action Uses: 2. Immediately after another creature's turn, The dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Pounce. The dragon moves up to half its Speed, and it makes one Rend attack.

Burst. The dragon uses the Heartburster attack on one marked creature in range.