Ancient Sea Dragon

Gargantuan Dragon Neutral Evil

• Armor Class: 22 (natural armor)
• Hit Points: 518 (28d20 + 224)
• Speed: walk 80 ft. fly 40 ft.
• Challenge Rating: 23 (50,000 XP)
• Source: Tome of Beasts 2023, page 125

• Saving Throws: Dex +7, Con +15, Wis +10, Cha +12
• Skills: Perception +17, Stealth +7
• Damage Vulnerabilities: False
• Damage Immunities: cold
• Damage Resistances: False
• Condition Immunities: False
• Senses: blindsight 60 ft., darkvision 120 ft., passive Perception 27
• Languages: Common, Draconic, Primordial

Special Abilities

• Amphibious: The dragon can breathe air and water.
• Legendary Resistance (3/Day): If the dragon fails a saving throw, it can choose to succeed instead.
• Siege Monster: The dragon deals double damage to objects and structures.

Actions

• Multiattack: The dragon uses its Frightful Presence. It then makes one Bite attack and two Fin attacks.
• Bite: Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 20 (2d10 + 9) piercing damage plus 14 (4d6) cold damage.
• Fin: Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 16 (2d6 + 9) slashing damage.
• Tail: Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 18 (2d8 + 9) 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 20 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.
• Tidal Breath (Recharge 5-6): The dragon exhales a crushing wave of frigid seawater in a 90-foot cone. Each creature in that area must make a DC 23 Dexterity saving throw. On a failure, the creature takes 44 (8d10) bludgeoning damage and 44 (8d10) cold damage and is pushed up to 45 feet away from the dragon and knocked prone. On a success, the creature takes half the damage and isn't pushed or knocked prone.

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.

Legendary Actions

• 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 15 feet of the dragon must succeed on a DC 24 Dexterity saving throw or take 16 (2d6 + 9) bludgeoning damage and be knocked prone. The dragon can then move up to half its flying speed, or swimming speed if in the water.

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