Black Dragon Lord

Amphibious. The dragon can breathe air and water.

Aura of Acid. So long as the dragon has at least 1 hit point, any creature that hits the dragon with a melee attack within 10 feet takes 11 (2d10) acid damage.

Chromatic Awakening (Recharges after a Short or Long Rest). If the dragon would be reduced to 0 hit points, its current hit point total instead resets to 500 hit points, it recharges its Breath Weapon, and it regains any expended uses of Legendary Resistance. Additionally, the dragon can now use the options in the “Mythic Actions” section for 1 hour.

Colossal. The dragon is one size category bigger then Gargantuan.

Innate Spellcasting. The dragon’s spellcasting ability is Charisma (spell save DC 26, +18 to hit with spell attacks). The dragon can innately cast the following spells, requiring no material components:

At Will: Blindness/Deafness, Create or Destroy Water, Darkness, Insect Plague, Mage Hand (the hand is invisible), Plant Growth, Thaumaturgy

3/day each: Contagion, Greater Invisibility (self only)

Keen Smell. The dragon has advantage on Wisdom (Perception) checks that rely on smell.

Legendary Resistance (5/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Magic Resistance. The dragon has advantage on saving throws against spells and other magical effects.

Magic Weapons. The dragon's attacks are considered magical.

Regeneration. The dragon regains 10 hit points at the start of each of its turns if it has at least 1 hit point.

Siege Monster. The dragon deals double damage to objects and structures.

Unusual Nature. The dragon does not require air, food, drink, or sleep.

Multiattack. The dragon can use its Frightful Presence. It then makes four attacks: one with its Bite, two with its Claws, and one with its Tail.

Bite. Melee Weapon Attack: +19 to hit, reach 30 ft., one target. Hit: 29 (3d12 + 10) piercing damage plus 22 (4d10) acid damage.

Claw. Melee Weapon Attack: +19 to hit, reach 25 ft., one target. Hit: 23 (3d8 + 10) slashing damage. On a hit, if the target is Huge or smaller, it is grappled (escape DC 20) and is restrained until this grapple ends. The dragon has two claws, each claw can grappled one target at a time.

Tail. Melee Weapon Attack: +19 to hit, reach 40 ft., one target. Hit: 26 (3d10 + 10) bludgeoning damage. On a Hit, the target must succeed on a DC 27 Strength saving throw. On a failed save, the target is knocked prone. If a target fails its saving throw by 5 or more, it is also pushed up to 60 feet away from the dragon. If a pushed target strikes a solid surface, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was pushed. If the target is pushed at another creature, that creature must succeed on a DC 27 Dexterity saving throw or take the same damage and be knocked prone.

Frightful Presence. Each creature of the dragon's choice that is within 150 feet of the dragon and aware of it must succeed on a DC 26 Wisdom saving throw. On a failed save, a creature is frightened for 1 minute. A frightened 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 an acidic blast in a 300–foot cone. Each creature in that area must make a DC 27 Dexterity saving throw. On a failed save, a creature takes 110 (20d10) acid damage and another 27 (5d10) acid damage at the end of its next turn. On a successful save a creature takes half damage and no damage at the end of its next turn.

Melting Corrosion (1/Day). The dragon summons a massive acidic sickly yellow mist in a 300–foot–radius sphere centered on the dragon. The acidic mist last for 1 minute, spreads around corners, and its area is lightly obscured. The acidic mist does not move with the dragon. Any creature that starts its turn in the cloud or enters the area for the first time on its turn must succeed on a DC 27 Constitution saving throw. On a failed save, a creature takes 55 (10d10) acid damage, and it cannot regain hit points until the start of its next turn. On a successful save, the target takes half damage with no additional effects. Creatures that have resistance to acid damage have advantage on the saving throw; creatures that have immunity to acid damage succeed automatically.

Change Shape. The dragon magically transforms into any beast or humanoid that is Large or smaller, while retaining its game statistics (other than its size). This transformation ends if the dragon is reduced to 0 hit points or uses its action to end it.

The dragon can take 5 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 each of its turns.

Attack. The dragon makes one Claw or Tail attack.

At–Will Spell. The dragon casts one of its “At–Will” spells, from its Innate Spellcasting list.

Detect. The dragon makes a Wisdom (Perception) check.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 30 feet of it must succeed on a DC 27 Dexterity saving throw. On a failed save, a creature takes 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Acid Spear (Costs 3 Actions). The dragon creates five spears of magical acid. Each spear fires towards a target of the dragon’s choice it can see within 300 feet of it. A target must succeed of a DC 26 Dexterity saving throw. On a failed save, a creature takes 9 (2d8) piercing damage and 9 (2d8) acid damage.

If the dragon’s Chromatic Awakening trait has activated in the last hour, it can use the options below as legendary actions.

Bite. The dragon makes one Bite attack.

Chromatic Flare (Costs 2 Actions). The dragon flares with elemental energy. Each creature in an 80–foot–radius sphere centered on the dragon must succeed on a DC 26 Dexterity saving throw. On a failed save, a creature takes 22 (4d10) acid damage. On a successful save, a creature takes half damage.