Tunneler.

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

Actions

Bite.

Melee Weapon Attack: +4 to hit, reach 10 ft., one target. Hit: 7 (1d10 + 2) piercing damage plus 3 (1d6) psychic damage.

Disorienting Breath (Recharge 5–6).

The dragon exhales a wave of psychic dissonance in a 15-foot cone. Each creature in that area must make a DC 12 Intelligence saving throw. On a failed save, the creature takes 17 (5d6) psychic damage, and until the end of its next turn, when the creature makes an attack roll or an ability check, it must roll a d4 and reduce the total by the number rolled. On a successful save, the creature takes half as much damage with no additional effects.

Spellcasting (Psionics).

The dragon casts one of the following spells, requiring no spell components and using Intelligence as the spellcasting ability (spell save DC 12):

At will: mage hand (the hand is invisible), minor illusion

Emerald Dragon Wyrmling