Ancient Stone Dragon

 Stone Skinned: Stone dragons have advantage on stealth checks when in rocky areas. Also when they are attacked by a unarmed strike the attacker takes 2d12 bludgeoning damage if they did not hit. When they are attacked with a weapon roll a d20. On a one the weapon breaks in half and is rendered useless.

Magical Sleep: If this does not encounter any hostile or friendly creature for one day it falls asleep. It wakes up when it is attacked or touched. During this time it appears as a statue.

Legendary Resistance(Three a Day): The dragon can chose to succeed a saving throw that he failed.

Multiattack. The dragon makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 30 (4d10 + 10) piercing damage plus 12 (4d6) fire damage.

Claw. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 22 (4d6 + 10) slashing damage.

Tail. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 22 (4d6 + 10)  bludgeoning damage

Stone Breath (Recharge 5–6). The dragon exhales hot rocks in a 60-foot cone. Each creature in that area must make a DC 18 Dexterity saving throw, taking 42 (14d6) fire damage and 42(14d6)bludgeoning damage on a failed save, or half as much damage on a successful one.

Petrifying Breath (Recharge 5–6). The dragon exhales a purple gas in a 40-foot cone. Each creature in that cone must make a Constitution saving throw 18 or become restrained. At the start of their next turn they must repeat the saving throw becoming unrestrained on a success and becoming petrified on a fail. The petrified creature can be unpetrified by using a greater restoration spell or a spell of similar power on the creature.

 Tough: The dragon can chose to not take damage from an attack. (Once per Day.)

 This ancient stone dragon has five legendary action points. The dragon can take a legendary action after another creature ends it's turn.

Tail (Cost One Action): The dragon makes a tail attack

Fortify (Cost Two Actions): The dragon makes a large wall of stone that is up to 30ft tall and up to 20ft. long and up to 10ft. thick in any space. If a creature is in this space that creature must make a Dexterity saving throw 18 or take 8d6 bludgeoning damage and move to any unoccupied space adjacent to where they used to be and the wall. They also become prone. On a success they must move 5ft. in any direction away from the wall. The dragon can spend a bonus action to make a wall made this way disappear. The wall last 1d4 days after the dragons death if it was never dispelled.

Stoney Gaze (Cost Two Action): The dragon choses a creature that he can see that can also see him. That creature must make a Constitution saving throw 18 or become petrified. A greater restoration spell or similar magic can undo this.

Stone Worker (Cost Three Actions):  The dragon can chose up to three petrified creatures that it can see to become under his control. This control ends when the creature is unpetrified or when the creature drops to zero hit points causing the body to shatter in to a thousand stone pieces. 

Empower (Cost Two Actions):  The dragon can use his mythic actions until the start of his next round.

 This adult stone dragon has one Mythic action point.

 Recharge: The dragon may recharge one of his breath weapons. If both are charged the dragon may use one of his breath weapons.