Karkethzerethzerus, the Sable Despoiler

Gargantuan Dragon, Lawful Good

Armor Class 22 (natural armor)

Hit Points 487 (25d20 + 225)

Speed 40 ft., fly 80 ft.

STR

+10

DEX

CON

INT

WIS

CHA

Saving Throws DEX +7, CON +16, WIS +9, CHA +13

Skills Arcana +11, History +11, Perception +16, Stealth +7

Damage Resistances necrotic

Damage Immunities cold

Senses blindsight 60 ft., darkvision 120 ft., passive Perception 26

Languages Common, Draconic

Challenge 23 (50,000 XP)

Traits

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

Living Shadow. While in dim light or darkness, the dragon has resistance to damage that isn't force, psychic, or radiant.

Shadow Stealth. While in dim light or darkness, the dragon can take the Hide action as a bonus action.

Sunlight Sensitivity. While in sunlight, the dragon has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Actions

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

Bite. Melee Weapon Attack: +17 to hit, reach 15 ft., one target. Hit:21 (2d10 + 10) piercing damage.

Claw. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit:17 (2d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit:19 (2d8 + 10) 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 21 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.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

The dragon exhales an icy blast in a 90-foot cone. Each creature in that area must make a DC 24 Constitution saving throw, taking 67 (15d8) necrotic damage on a failed save, or half as much damage on a successful one. A humanoid reduced to 0 hit points by this damage dies, and an undead shadow rises from its corpse and acts immediately after the dragon in the initiative count. The shadow is under the dragon's control.
The dragon exhales paralyzing gas in a 90-foot cone. Each creature in that area must succeed on a DC 24 Constitution saving throw or be paralyzed 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.

Change Shape. The dragon magically polymorphs into a humanoid or beast that has a challenge rating no higher than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (the dragon's choice).

In a new form, the dragon retains its alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, lair actions, and Intelligence, Wisdom, and Charisma scores, as well as this action. Its statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

Legendary Actions

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

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.