Valamir, the Blood Drinker

Amphibious. The dragon can breathe air and water.

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

Multiattack. The dragon can use its Frightful Presence. It then makes two attacks: one with its bite and one with its claws or one with its tail.

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 4 (1d8) acid damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

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 16 Wisdom saving throw or become frightened 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.

Acid Breath (Recharge 5–6). The dragon exhales acid in a 60-­foot line that is 5 feet wide. Each creature in that line must make a DC 18 Dexterity saving throw, taking 45 (10d8) acid damage on a failed save, or half as much damage on a successful one.

Curse of The Blood. When a creature lands the killing blow on Valamir, he utters one final phrase before dying, imparting a curse from the following table. Roll a 1d4.

1. Dark Healing. You are no longer able to heal through normal means and any attempt to heal that way instead damages you. Instead, you can now only heal through Necrotic damage or Acid damage (DMs choice).
2. Deep Cuts. Whenever you take melee damage your wounds are deeper than normal. Take an additional 1d4 points of damage per each attack that successfully manages to hit you.
3. Bad Luck. You gain a -1 penalty on all attacks, damage, saves, skill and ability checks.
4. Madness Upon You. Roll on the Long Term Madness table. 

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.

Tail Attack. The dragon makes a tail attack.

Bellow (Costs 2 Actions). The dragon bellows loudly, calling for nearby aid within a 120-foot range, raising 2d8 Skeletons.

Scale Attack (Costs 2 Actions). The dragon beats its wings, causing projectile scales to fly in a 30-foot cone. Each creature within that area must succeed on a DC 15 Dexterity saving throw or take 22 (5d8 + 6) piercing damage or half as much on a successful save. The dragon can then fly up to half its flying speed.

Bone Armor (Costs 3 Actions). The dragon gathers nearby skeleton or other corpses and shoved them into the crevices of its body, filling in wounds. This gives the Dragon a +2 to AC until the end of its next turn, as well as heal it for 4d8 health.