Tunneler. The dragon can burrow through solid rock at half its burrowing speed and leaves a 10-foot-diameter tunnel in its wake.

Unusual Nature. The dragon doesn't require air.

Multiattack. The dragon makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit:7 (1d6 + 4) piercing damage plus 3 (1d6) cold damage.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit:7 (1d6 + 4) slashing damage.

Cold Breath (Recharge 5–6). The dragon exhales a blast of frost in a 30-foot cone. Each creature in the cone must make a DC 15 Constitution saving throw. On a failed save, the creature takes 27 (6d8) cold damage, and its speed is halved until the end of its next turn. On a successful save, the creature takes half as much damage, and its speed isn't reduced.

Phase (2/Day). The dragon becomes partially incorporeal for as long as it maintains concentration on the effect (as if concentrating on a spell). While partially incorporeal, the dragon has resistance to bludgeoning, piercing, and slashing damage.