See ethereal. The ethereal dragon can see into the ethereal plane around their location. 

Ethereal immunity. The ethereal dragon is immune to all natural harmful effects in the ethereal plane for example ethereal cyclones don't effect them. 

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Multiattack. The adult ethereal dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., 1 target. Hit: 15 (2d10 + 4) piercing damage. 

Claw. Melee Weapon Attack: +9 to hit, reach 5 ft., 1 target. Hit: 11 (2d6 + 4) slashing damage. 

Tail. Melee Weapon Attack: +9 to hit, reach 10 ft., 1 target. Hit: 13 (2d8 + 4) bludgeoning damage. 

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 15 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Ethereal force breath (Recharge on 5/6). The ethereal dragon exhales a blast of cyan energy in a 60ft cone. Each creature that is within range must make a DC 16 Constitution saving throw or take 59 (17d6) force damage. This breath weapon also hits targets on the ethereal plane and on a successful saving throw a creature takes half damage. 

The adult ethereal dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time, and only at the end of another creature’s turn. The adult ethereal dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Ethereal switch (Costs 2 Actions). The ethereal dragon shifts what plane of existence its on to either the material plane or the ethereal plane.