Multiattack

The dragon uses its Frightful Presence. It then makes one Bite attack and two Claw attacks.

Bite

Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage. Instead of dealing damage, the dragon can end one magical effect of its choice of 5th level or lower on the target.

Claw

Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 13 (2d6 +6) slashing damage, and if the target isn't a Construct or Undead, it must succeed on a DC 19 Constitution saving throw or lose 7 (2d6) hp at the start of each of its turns as a piece of metallic claw breaks off in the wound. Any creature can take an action to remove the claw with a successful DC 14 Wisdom (Medicine) check. The claw pops out of the wound if the target receives magical healing.

Tail

Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) 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 18 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end 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.

Shard Breath (Recharge 5-6)

The mithral dragon spits metallic shards in a 60-foot cone. Each creature in that area must make a DC 19 Constitution saving throw, taking 42 (12d6) slashing damage on a failed save, or half as much on a successful one. The area becomes difficult terrain for 1 minute, then the shards dissolve into wisps of silvery smoke. When a creature moves into or within the area, it takes 7 (2d6) slashing damage for every 5 feet it travels.