The Quiet Ones
Quiet One, Adult CR: 8
No Breathing. The Quiet One doesn't need to breath and are unaffected by poisons in the air. Quiet. The Quiet Ones are totally quiet. Even when digging they cannot be heard even by the sharpest ears. Disintegrate Immunity. The Quiet One uses disintegrate magic to dig through the earth and has gained immunity to the spell.
Disintegrate (4-6) The Quiet one unleashes a green cloud of disintegrating magic directly in front of it. All creations of magical force and non-magical objects, not being carried, in the area are disintegrated. Any creature in the area can make a DC 15 dexterity saving throw to try to jump out of the area to a space within 5 ft of it. A creature which has no place to jump to automatically fails the save. On a failed save the creature takes 4d6+20 force damage. If this damage reduces the target to 0 hit points, it is disintegrated. A disintegrated creature and everything it is wearing and carrying, except magic items, are reduced to a pile of fine gray dust. The creature can be restored to life only by means of a true resurrection or a wish spell.