Legendary Resistance (3/Day, or 4/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.

Amphibious. The dragon can breathe both air and water.

Multiattack. The dragon makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 7) piercing damage.

Claw. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage.

Steam Breath (Recharge 5-6). The dragon expels superheated steam in a 10 foot wide, 60-foot-long line. Anyone caught in the area must make a dexterity saving throw, dc 16, taking 30 (6d6 + 4) fire damage on a failed save, or half as much on a success.

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Tsunami. The dragon creates a tsunami-like wave that crashes down in a 30-foot cube in front of it. Any creatures within this area must make a dexterity saving throw or take 4d8 bludgeoning damage and 3d6 slashing damage. This damage is increased to 5d8 and 4d6 when it is in its lair.

Dive. The dragon dives down into the swirling waters around it, moving up to 60 feet before emerging. This displaces any creatures within 10 feet of the dragon, pushing them 15 feet away from the dragon. This also deals 3d6 slashing damage to any affected creatures.

Surf. The dragon moves up to half its Speed, and it makes one Rend attack.