Lunar Dragon Wyrmling

The dragon can burrow through solid rock at half its burrowing speed and leaves a 5-foot-diameter tunnel in its wake.

The dragon doesn't require air.

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage plus 3 (1d6) cold damage.

The dragon exhales a blast of frost in a 15-foot cone. Each creature in the cone must make a DC 13 Constitution saving throw. On a failed save, the creature takes 13 (3d8) 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.

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.