Amphibious. The dragon can breathe air and water.

Innate Spellcasting. The dragon's innate spellcasting ability is Wisdom (spell save DC 19, +11 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: detect magic, earth tremor, faerie fire
3/day each: heat metal, hold person, pass without trace
1/day each: polymorph, freedom of movement, mass cure wounds

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

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its prow 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) fire 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.

Roiling Amber Breath (Recharge 5–6). The dragon exhales liquid amber in a 30-­foot cone. Each creature in that line must make a DC 18 Dexterity saving throw, taking 54 (12d8) fire damage on a failed save, or half as much damage on a successful one. The creature must then make a DC 18CON save or be immobilized within an encasement of amber, and be considered restrained and begins to suffocate. The amber has an AC of 15 and 10 hit points. 

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.