ancient diamond dragon

Death Burst. When the Dragon dies, it explodes in a burst of light and fire. Each creature within 100 feet of it must make a DC 22 Dexterity saving throw, taking (7d6) fire damage and (7d6) radiant damage on a failed save, or half as much damage on a successful one. Flammable objects that aren't being worn or carried in that area are ignited. In the center were the dragon once stood, a Diamond Dragon Heart is left.

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

Radiant Reflection. Whenever the dragon is subjected to radiant damage, it takes half damage and redirects the other half to the attacker.

Reflective Scales. Any time the Dragon is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d4. On a 1 to 3, the Dragon is unaffected. On a 4, the Dragon is unaffected, and the effect is reflected back at the caster as though it originated from the Dragon, turning the caster into the target.

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

Multiattack. The dragon uses its Frightful Presence if it can. It then makes three attacks: one with its bite and two with its claws and 1 with its tail.

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

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 24 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.

Fire Breath. The dragon exhales fire in a 120-foot cone. Each creature in that area must make a DC 25 Dexterity saving throw, taking (15d10) fire damage on a failed save, or half as much damage on a successful one.

 Petrifying Breath. The dragon exhales gas in a 120-foot cone. Each creature in that area must succeed on a DC 25 Constitution saving throw or be petrified until removed by Greater Restoration or another spell of 5th level or higher (Magic items work to). 

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

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.

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 (5d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Breath Weapon. (Costs 3 Actions). Roll a d20, if 1-15 you do nothing and you wasted a legendary action. If 16-20, you use either one of your breath weapons.