# 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

| STR | DEX | CON | INT | WIS | CHA |
| --- | --- | --- | --- | --- | --- |
| 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 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.