Earth Glide.

The dao can burrow through nonmagical, unworked earth and stone. While doing so, the dao doesn't disturb the material it moves through.

Elemental Demise.

If the dao dies, its body disintegrates into crystalline powder, leaving behind only equipment the dao was wearing or carrying.

Innate Spellcasting.

The dao's innate spellcasting ability is Charisma (spell save DC 14, +6 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: detect evil and good, detect magic, stone shape
3/day each: passwall, move earth, tongues
1/day each: conjure elemental (earth elemental only), gaseous form, invisibility, phantasmal killer, plane shift, wall of stone

Sure-Footed.

The dao has advantage on Strength and Dexterity saving throws made against effects that would knock it prone.

Actions

Multiattack.

The Dao makes two fist attacks or two maul attacks.

Fist.

Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

Maul.

Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 20 (4d6 + 6) bludgeoning damage. If the target is a Huge or smaller creature, it must succeed on a DC 18 Strength check or be knocked prone.