Multiattack

The dragon makes one Bite attack and two Fin attacks.

Bite

Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 16 (2d10 + 5) piercing damage plus 7 (2d6) cold damage.

Fin

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage.

Tidal Breath (Recharge 5-6)

The dragon exhales a crushing wave of frigid seawater in a 30-foot cone. Each creature in that area must make a DC 16 Dexterity saving throw. On a failure, the creature takes 22 (4d10) bludgeoning damage and 22 (4d10) cold damage and is pushed up to 15 feet away from the dragon and knocked prone. On a success, the creature takes half the damage and isn't pushed or knocked prone.