Innate Spellcasting (Psionics). The dragon’s innate spellcasting ability is Intelligence (spell save DC 17). It can innately cast the following spells, requiring no components:
1/day each: scrying, telekinesis, teleportation circle
Legendary Resistance (2/Day). If the dragon fails a saving throw, it can choose to succeed instead.
Spider Climb. The dragon can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Tunneler. The dragon can burrow through solid rock at half its burrow speed and can choose to leave a 10-foot-diameter tunnel in its wake.
Multiattack. The dragon can use its Frightful Presence. It then makes two melee attacks, one with its bite and one with its claws.
Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 3 (1d6) thunder damage.
Claws. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 19 (3d8 + 6) slashing damage.
Tail. Melee Weapon Attack: +11 to hit, reach 10 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 17 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.
Debilitating Breath (Recharge 5–6). The dragon exhales a 20ft radius sphere pulse of high-pitched, nearly inaudible sound at a point it can see within 120ft. Each creature in the area must make a DC 18 Constitution saving throw. On a failed save, the creature takes 45 (13d6) thunder damage and is incapacitated until the end of its next turn. On a successful save, the creature takes half as much damage and isn’t incapacitated, other gem dragons are immune to this breath weapon..
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.
Tail Attack. The dragon makes a tail attack.
Telekinetic Fling. The dragon chooses a Small or smaller object that isn’t being worn or carried that it can see within 60 feet of it, and it magically hurls the object at a creature it can see within 60 feet of the object. The target must succeed on a DC 17 Dexterity saving throw or take 14 (4d6) bludgeoning damage.
Teleport (Costs 2 Actions). The dragon magically teleports to an unoccupied space it can see within 30 feet of it.