Young Sea Dragon
Large Dragon, neutral evil
Armor Class 18 (natural armor)
Hit Points 152 (16d10+64)
Speed fly +80, swim +50, walk +40
Challenge 9
Saving Throws cha +7, con +8, dex +4, wis +5
Skills stealth +4, perception +9
Damage Immunities cold
Senses blindsight 30 ft. darkvision 120 ft., passive Perception 19
Languages Common, Draconic
Special Abilities
Amphibious. The dragon can breathe air and water.
Siege Monster. The dragon deals double damage to objects and structures
Actions
Multiattack. The dragon makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 16 (2d10 + 5) piercing damage plus 5 (1d10) cold damage.
Claw. 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 target takes 27 (5d10) bludgeoning damage and 27 (5d10) cold damage, and is pushed 30 feet away from the dragon and knocked prone. On a successful save the creature takes half as much damage and isn't pushed or knocked prone.
Source: Tome of Beasts · OGL/Open