Amphibious. The dragon can breathe air and water.

Keen Eyesight. The dragon has advantage on Perception checks.

The Sound Of Silence. The dragon cannot hear and is considered deafened always.

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

Spellcasting. the dragon is a 8th-level spellcaster. its spellcasting ability is Charisma (spell save DC 19, +9 to hit with spell attacks). He has the following wizard spells prepared:

Cantrips (at will): minor illusion message

1st level (4 slots): color spray, dissonant whispers, hideous laughter

2nd level (3 slots): blur,  mirror image, blindness/deafness, misty step, phantasmal force

3rd level (3 slots): blink, enemies abound, glyph of warding, hypnotic pattern

4th level (2 slots): banishment, phantasmal killer, fabricate

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

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 4 (1d8) force damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) 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 16 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.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

Force Breath. The dragon exhales pure magical force in an 60-foot line that is 15 feet wide. Each creature in that line must make a DC 19 Intelligence saving throw, taking 66 (12d10) force damage on a failed save, or half as much damage on a successful one.

Blinding Breath. The dragon exhales fine particles of dust in a 20-foot cone. Each creature in that area must succeed on a DC 19 Constitution saving throw or become blinded for 1 minute. This effect ends for a creature if the creature succeeds on a DC 19 Wisdom saving throw or if the blindness is cured, magical or otherwise.

Invisibility. The dragon turns invisible, as if using the greater invisibility spell. 

The 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 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.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.