Ancient Sea Dragon

Gargantuan dragon, neutral evil

Armor Class 22 (natural armor)

Hit Points 481 (26d20 + 208)

Speed 40 ft., fly 80 ft., swim 80 ft.

29 (+9) 10 (+0) 27 (+8) 19 (+4) 17 (+3) 21 (+5)

Saving Throws Dex +7, Con +15, Wis +10, Cha +12

Skills Perception +17, Stealth +7

Damage Immunities cold

Senses blindsight 60 ft., darkvision 120 ft., passive Perception 27

Languages Common, Draconic, Infernal, Primordial

Challenge 22 (41,000 XP)

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.


Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 20 (2d10 + 9) piercing damage plus 11 (2d10) cold damage.

Claw. 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 repeats 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 target takes 44 (8d10) bludgeoning damage and 44 (8d10) 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.

Legendary Actions

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.

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 swim speed if in the water.