Ancient Sea King

• Saving Throws Dex +8, Con +16, Wis +11
• Damage Resistances cold, fire
• Senses truesight 120 ft., passive Perception 21
• Languages Sea King, Telepathy 120 ft. (with others that can hear the "voice of all things")
• Challenge 24 (62,000 XP)

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  Amphibious. The sea king can breathe air and water.

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

  Rage of The Sea (Recharges after a Short or Long Rest). If the sea king would be reduced to 0 Hit Points, its current hit point total instead resets to 350 Hit Points, and it recharges its Seawater Cannon. Additionally, the sea king can now use the options in the “Mythic Actions” section for 1 hour. Award a party an additional 62,000 XP (124,000 XP total) for defeating the sea king after its Rage of The Sea activates.

  Siege Monster. The sea king deals double damage to objects and structures.

Multiattack. The sea king can make one Bite attack and one Constrict or Tail attack.

Bite. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: (2d12 + 9) piercing damage plus (1d12) cold damage.

Constrict. Melee Weapon Attack: +16 to hit, reach 5 ft., one target. Hit: (4d10 + 9) bludgeoning damage, and the target is grappled (escape DC 24). Until this grapple ends, the creature is restrained, and the sea king can’t constrict another target.

Tail. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: (2d12 + 9) bludgeoning damage. If the target is a creature, it must succeed on a DC 24 Strength saving throw or be knocked prone.

Seawater Cannon (Recharge 5-6). The sea king exhales a 90-foot cone wave of frigid seawater. Each creature in that area must make a DC 24 Dexterity saving throw. On a failure, the target takes 44 (8d10) bludgeoning damage and 44 (8d10) cold damage, and is pushed 15 feet away from the sea king and knocked prone. On a successful save the creature takes half as much damage and isn’t pushed or knocked prone.

Enter the description for how bonus actions work for your monster here.

The sea king 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 sea king regains spent legendary actions at the start of its turn.

• Tail. The sea king makes one Tail attack.
• Move. The sea king moves up to its speed. If the sea king is swimming, this movement doesn’t provoke opportunity attacks.
• Tidal Wave (Costs 3 Actions). The sea king unleashes a wave of water that crashes down in a 90-foot line that is 10 feet wide and 10 feet tall. Each creature in that area must make a DC 24 Dexterity saving throw, taking 11 (2d10) bludgeoning damage and 11 (2d10) cold damage on a failed save, or half as much damage on a successful one.

If the sea king’s Rage of the Sea trait has activated in the last hour, it can use the options below as legendary actions.

• Bite. The sea king makes one Bite attack.
• Roar of Storms (Costs 2 Actions). The sea king unleashes a magical roar. Each creature in a 60-foot-radius sphere centered on the sea king must succeed on a DC 24 Constitution saving throw or take 16 (3d10) thunder damage and be knocked prone.