Ancient Adamantine Dragon

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

Stone Camoflouge. The dragon Dexterity (Stealth) checks made to hide in rocky terrain. 

Obvious Leadership. All other dragonkin automatically fail Charisma (Intimidation) checks towards the dragon. 

Shattering Demise. When the Adamantine dragon is killed it explodes into razor-sharp spikes of adamantine. Treat the area where these spikes hit the ground like a spike growth zone that does 3d8 piercing damage (This damage is magical). 

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: +18 to hit, reach 15 ft., one target. Hit:  20 (3d10 + 10) piercing damage. 

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit:  14 (3d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit:  17 (3d8 + 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 25 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 saving throw is successful or the effect ends for it, the creature is immune to the dragons Frightful Presence for the next 24 hours. 

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

Acid Breath. The dragon exhales acid in a 90-foot line that is 20 feet wide. Each creature in that area must make a DC 25 Dexterity saving throw, taking 100 (20d10) acid damage on a failed save, or half as much on a successful one. Additionally, on a failed save, if the creature is wearing metal armor, the metal corrodes and gains a permanent and cumulative -1 penalty to the AC it has to offer. If the penalty drops to -5, the armor is destroyed. 

Sickening Breath. The dragon exhales a noxious fog in a 90-foot cone. Each creature in that area must make a DC 25 Constitution saving throw, taking 100 (20d10) poison damage on a failed save, or half as much on a successful on. Additionally, on a failed save, The creature is poisoned. While poisoned in this way, the creature has disadvantage on attack rolls and gains a -1 penalty to its Strenght and Constitution score. This reduction lasts until the creature finishes a long rest. 

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 dragons 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 for any class features or legendary actions of that form. 

Reaction Name. Enter the description for your action.

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

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 26 Dexterity saving throw or take 14 (3d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.