Livyathan

Gargantuan aberration-dragon, lawful evil

Armor Class 19 (natural armor)
Hit Points 350 (21d20+126)
Speed 40 ft., swim 80ft., fly 80ft.

STR	DEX	CON	INT	WIS	CHA
27 (+8)	8 (-1)	23 (+6)	26 (+8)	17 (+3)	22 (+6)

Saving Throws Dex +6 Con +13 Wis +10
Skills Arcana +15, History +15, Perception +17
Damage Resistances bludgeoning, piercing, slashing from non-magical weapons
Damage Immunities cold, poison
Condition Immunities frightened, paralyzed, petrified, poisoned
Senses blindsight 60 ft., darkvision 120 ft., passive Perception 27
Languages Common, Deep Speech, Draconic, Primordial, Undercommon
Challenge 21 (33,000 XP)

SPECIAL Traits

• Legendary Resistance (3/Day). If the livyathan fails a saving throw, it can choose to succeed instead.
• Magic Resistance. The livyathan has advantage on saving throws against spells and other magical effects.
• Mental Fortress. The livyathan has advantage on Intelligence, Wisdom, and Charisma saving throws that are not the result of spells or magical effects.

ACTIONS

• Multiattack. A livyathan can use its horror, then makes three attacks: one with his bite and two with his tentacles.
• Bite. Melee Weapon Attack: +15 to hit, reach 10ft., one target. Hit: 19 (2d10+8) piercing damage, plus 7 (2d6) acid damage.
• Tentacle. Melee Weapon Attack: +15 to hit, reach 15ft., one target. Hit: 15 (2d6 + 8) bludgeoning damage. If the target is a creature, it must succeed on a DC 21 Constitution saving throw or become diseased. The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, the diseased creature’s skin becomes translucent and slimy, the creature can’t regain hit points unless it is underwater, and the disease can be removed only by heal or another disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6 (1d12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes have passed. The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, the diseased creature’s skin becomes translucent and slimy, the creature can’t regain hit points unless it is underwater, and the disease can be removed only by heal or another disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6 (1d12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes have passed.
• Tail. Melee Weapon Attack: +15 to hit, reach 15ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage. In addition, the target becomes grappled. If the target is a creature, it must succeed on a DC 21 Constitution saving throw or become diseased. The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, the diseased creature’s skin becomes translucent and slimy, the creature can’t regain hit points unless it is underwater, and the disease can be removed only by heal or another disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6 (1d12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes have passed.
• Battle Mind. The livyathan may create a telepathic link with a number of creatures it can see equal to its Intelligence score (26). These creatures are typically its field generals. Creatures included in battle mind may communicate telepathically with each other and the livyathan at any distance. Any creature included in battle mind has their proficiency bonus increased by 2 to a maximum of 7. As an action, the livyathan may perceive through the senses of one member of the battle mind. Each link continues until dismissed by the livyathan, the livyathan dies or goes unconscious, or until it is on a different plane of existence than the member.
• Horror. Each creature of the livyathan’s choice that is within 120 feet of it and aware of it must succeed on a DC 23 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 livyathan’s Horror for the next 24 hours.
• Acid Slime Breath (Recharge 5-6). The livyathan exhales a cone of acidic slime that coats all foes in a 60-foot cone that fail a DC 21 Dexterity save. Foes that fail the save take 63 (18d6) acid damage, or half as much on a successful save. All creatures caught within the cone must also make a DC 21 Constitution save or become diseased for 1d4 hours. Diseased creatures lose the ability to breathe air, but gain the ability to breathe water. In addition, if the breath weapon is used under water or targets foes within water, the slime separates into droplets on the following round, forming into an acidic jellyfish swarm.
• Enslave (3/Day). The livyathan targets one creature it can see within 60 feet of it. The target must succeed on a DC 23 Wisdom saving throw or be magically charmed until the livyathan dies or until the livyathan is on a different plane of existence from the target. The charmed target is under the livyathan’s control and can’t take reactions, and the livyathan and the target can communicate telepathically with each other over any distance. Whenever the charmed target takes damage, the target can repeat the saving throw. On a success, the effect ends. No more than once every 7 days, the target can also repeat the saving throw when it is at least 1 mile away from the livyathan.

LEGENDARY ACTIONS

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

• Detect. The livyathan makes a Wisdom (Perception) check.
• Tail Attack. The livyathan makes a tail attack.
• Wing Attack (Costs 2 Actions). The livyathan beats its wings. Each creature within 10 feet of the livyathan must succeed on a DC 21 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The livyathan can then fly up to half its flying speed.

LAIR ACTIONS

On initiative count 20 (losing initiative ties), the livyathan takes a lair action to cause one of the following effects; the dragon can’t use the same effect two rounds in a row:

• Superheated water and dissolved chemicals erupts from a point on the ground the livyathan can see within 120 feet of it, creating a 20-foot-high, 5-foot-radius hydrothermal vent plume (or geyser if on the surface). Each creature in the plume’s area must make a DC 21 Dexterity saving throw, taking 21 (6d6) fire damage on a failed save, or half as much damage on a successful one.
• A shockwave shakes the lair in a 60-foot radius around the livyathan sending powerful currents throughout the area. Each creature other than the livyathan in that area must succeed on a DC 21 Dexterity saving throw or be knocked prone (if underwater, creatures become disoriented, with the same game effects as being knocked prone).
• Hydrothermal gases form a cloud in a 20-foot-radius sphere centered on a point the livyathan can see within 120 feet of it. The sphere spreads around corners, and its area is lightly obscured. It lasts until initiative count 20 on the next round. Each creature that starts its turn in the cloud must succeed on a DC 21 Constitution saving throw or be poisoned for 1 minute. The creature may repeat the saving throw at the end of each of its turns to negate the effect.

REGIONAL EFFECTS

The region containing a livyathan’s lair is warped by the creature’s presence, which creates one or more of the following effects:

• Underground surfaces within 1 mile of the livyathan’s lair are slimy and wet and are difficult terrain.
• Water sources within 1 mile of the lair are supernaturally fouled. Enemies of the livyathan that drink such water vomit it within minutes.
• Deep sea fissures and hydrothermal vent fields appear within 1 mile of the livyathan’s lair.

If the livyathan dies, these effects fade over the course of 3d10 days.

ABOUT

The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, the diseased creature’s skin becomes translucent and slimy, the creature can’t regain hit points unless it is underwater, and the disease can be removed only by heal or another disease-curing spell of 6th level or higher. When the creature is outside a body of water, it takes 6 (1d12) acid damage every 10 minutes unless moisture is applied to the skin before 10 minutes have passed.