In this series I have been presenting creatures you can use for villains, lieutenants, minions, and wild encounters for 5th edition aquatic games, as well as encounter seeds for these villains at each tier. This article is the second presenting an outline for you to draw from when creating your own aquatic campaign!

Since the number of monsters for this highest tier is so limited, I’m combining the list of enemies for 16th-20th levels and the campaign seed into one post.

This week I bring you an aquatic campaign that culminates in facing one of the most terrifying and iconic aquatic villains, the aboleth, specifically, the livyathan created by Sam Hing for Rogue Genius Games’ “Horrors of the Aboleth“.

Though these monster lists and story seeds are inspired by 5th edition, they can be used as adventure ideas for any fantasy RPG.


Challenge Rating 17
  • Dracolich
Challenge Rating 18
  • Demilich
Challenge Rating 21
  • Black Dragon (Ancient)
  • Lich
Challenge Rating 22
  • Green Dragon (Ancient)
Challenge Rating 23
  • Kraken


Challenge Rating 11
  • Marid
Challenge Rating 12
  • Archmage (can be of any aquatic race or creature capable of having an Intelligence of 18 or higher; increase CR by 1 if already greater than 12) 
Challenge Rating 14
  • Black Dragon (Adult)
Challenge Rating 15
  • Green Dragon (Adult)


Challenge Rating 8
  • Assassin (any aquatic race or creature with Intelligence 12 or higher; increase CR by 1 if already greater than 8)
Challenge Rating 11
  • Marid
Challenge Rating 12
  • Archmage (can be of any aquatic race or creature capable of having an Intelligence of 18 or higher; increase CR by 1 if already greater than 12) 
Challenge Rating 13
  • Storm Giant
Challenge Rating 17
  • Dragon Turtle

Campaign Outline

Ancient Memories

Aberrant Threats

Aberrations are the classic horrors from the deep and represent a range of creatures, from intellect devourers and mind flayers, to slaadi and beholders. Even in a world where dragons roam the skies and where owlbears are an expected danger in any nearby forests, these twisted creatures are alien, originating from dark dimensions or even other planets depending on your setting and mythology. They are the Cthulhoid horrors of D&D and are ideal for aquatic campaigns.

Aboleth are slavers by inclination, seeing all creatures as beneath them. Their ancient empires crushed by the gods, the aboleth as a culture have attempted numerous times in history to reestablish their command of the world. A millennium ago, that attempt put them at odds with a draconic empire, and in the arm’s race that ensued, created an abomination of draconic size with all the psychic power of the aboleth; the livyathan.

For the purposes of this campaign, the aboleth that survived the draconic wars retreated to the depths of a labyrinthine complex of deep sea fissures known as The Trench. The Trench refers both to the vast maze of tectonic cracks, as well as to the city that has thrived there for centuries. The “city-state” of Trench is in fact far larger than any metropolis that surface dwellers can imagine, covering 50,000 square miles and reaching a depth of nearly 2 miles.

The current ruler of The Trench is an ancient, 950-year-old livyathan called Vargorish. Like all livyathans, Vargorish has a violent hatred of anything and anyone arrogant enough to think they aren’t under his rule. He has put a plan in motion to prove the surrounding marine countries wrong on that account. As livyathans and behemoths are far more mobile above the waves than their aboleth kin, Vargorish’s war won’t stop at coastlines.

Though Vargorish’s arrogance is vast, his intelligence dwarfs that of even the most ancient dragons. Because of that, he has made an unholy alliance with an Elder Brain that rules an aquatic mind flayer collective on the edges of the Trench. As both of these beings have psychic powers that would drive normal folk insane, they communicate almost exclusively through emissaries who are only aware of small sections of any larger plan. Of course, both rulers realize that the other will betray them at an opportune moment.

The city of the Elder Brain consists of ~300,000 sentient creatures; 25% mind flayers, 23% merrow, 10% scrags (trolls with the amphibious quality), 8% umbrals (aquatic umberhulks with crustacean features), 34% other humanoid/piscinoid slave races (cecaeliadeep merfolk, locathah, deep sea elves, koalinth, etc).

The population of the city-state of Trench has reached 1,000,000 sentient creatures; 21% aboleth (including sub-races such as the engulfer and manipulator), 62% ulat-kini, and 17% other humanoid/piscinoid slave races (cecaeliadeep merfolk, locathah, deep sea elves, koalinth, etc)]. Other sentient creatures include hundreds of aboleth behemoths being bred for war, scores of enslaved dragon turtles, and Vargorish’s children: four livyathans ranging from 25 years to 300 years old. Though half of the population is actively being prepared for war, only 400,000 are soldiers, with 100,00 acting in support roles.

About Numbers

These numbers aren’t intended to be set in stone, but to give you a place to start for your own campaign world. The the Incursion campaign framework presented in Dragon Magazine #309, and Dungeon Magazine #100 allows for a range of invading-army sizes, and with a force of thousands of soldiers able to control the minds of their enemies, even a much smaller initial population could result in a large invading force rather quickly.

1st-5th level

As with the Prodigal Son campaign outline, this tier should consist of a range of standard adventures that are sprinkled with encounters hinting at the horrors to come. Though the population of the city-state of Trench would shock any ruler who knew, that number is still only a fraction of the total population of the various marine kingdoms (as the estimated population of the continent of Faerun is near 70 million, the surface area of the oceans alone would at least double if not quadruple that number).

In order to increase their numbers, and recruit spies who are already familiar with the various cultures and societies in the photic zone, ulat-kini pilgrims have been slowly dispatched across the ocean. In the majority of kingdoms, the descendants of the aboleth’s former slaves, known as skum to those not from Trench, may exist in large numbers while being seen as lower-class citizens, menial laborers, servants, and depending on the country, even slaves. The ulat-kini pilgrims are far more intelligent and charismatic than the crushed souls of the most common skum. These leaders will instill hope in their long-“lost” brothers and sisters, gathering them in secret societies that teach the true and proud history of their ancestors. These Cults of the Ancients can be uncovered by the PCs in their local settlement, perhaps being led by one or more mind flayers, and should include non-skum members as well.

The party may even cross the path of a group of adventurers in the service of the flayers, who in turn are serving aboleth lieutenants. This group should include one or more ulat-kini that have more power, skill, and confidence than any other skum the party has met, signaling that something strange is happening.

6th-10th level

At this level, Vargorish’s plans involve the active infiltration of nearby countries, as well as the testing of several critical WMDs. Once the Invisible Army of skum are unified across the seas, doppleganger spies allied to the Elder Brain will move into key, influential positions. If the party dismantled one or more of the Cult cells, then placing an agent close to the party would be a priority as well.

The Mining Gambit

Though Vargorish’s minions have drawn hordes of skum into fanatical devotion to the Cult, he needs to train large numbers of these soldiers in mass combat techniques. He also knows that the disappearance of large numbers of skum from metropolitan districts would cause far too much suspicion. Luckily for him, one of the largest communities of skum (over 20,000 strong) are slaves in the mines of kraken-ruled country that he needs to undermine. The economy of this country is largely dependent on the mine’s production so Vargorish puts a plan into motion that will get him his soldiers, test a brutal weapon, and put the resources of one of his most powerful rivals into turmoil.

  1. Aboleth manipulators, powerful psychics and arcane researchers, have discovered a way to enhance the telekinetic powers of certain aboleth with sorcery. When enough of these enhanced telekinetics work together, they believe they can shift tectonic plates, causing massive earthquakes wherever they choose. But they need to test it without arousing too much suspicion.
  2. Hundreds of ulat-kini pilgrims have allowed themselves to be taken as slaves over the past year and are in telepathic communication with their masters. The pilgrims have brought thousands of their kin into the Cult of the Ancients in that time, with hundreds more joining every week.
  3. Aboleth engineers and mind-flayer slave drivers spent the year forcing scores of umbrals to dig caverns from the Void (a 20-mile-long volcanic ridge, home to hundreds of hydrothermal vent fields spewing miles of visibility-limiting clouds into the surrounding water) to the farthest edge of the mines.
  4. When the time is right, the pilgrims will lead the thousands of their followers working in the mines to rebel against their slavemasters in the far-reaches of the mines, then herd the to the umbral tunnels. Then the enhanced telekinetics will cause the largest portions of the mines to collapse, burying any sign of rebellion and escape, as well as setting the country’s economy into ruin.

The PCs may uncover parts of this plot at any of its early stages.

  1. The same party of ulat-kini adventurers (or a new group if the original was defeated) may be sent to recover an artifact, material components, or psychic repository from the ruins of an aboleth city. The item(s) may be needed as the final component to enhance the aboleth telekinetics.
  2. Clues may lead the PCs to the spread of the Cult into the mines of Kraken country. The PCs may have to decide whether to stop the cult and leave the skum to their life of slavery, or to leave the cult be, undermine a powerful and evil country, while not fully understanding their actions will boost the numbers of a far larger threat.
  3. PCs may be sent to the Void on an unrelated quest, only to discover the aboleth/umbral mining operation.

11th-15th level

At this tier, the party will discover the existence of the Trench and the scope of the threat the city-state poses. Early adventures may include investigating one or more ruined aboleth cities which hold clues to the existence of livyathans, or even making contact with an ancient gold, bronze, black, or green dragon that lived through the draco-aboleth wars. Once the existence of the Trench is in the party’s hands, they will likely wish to scout the place out, only to find a massive, cosmopolitan city-state prepped for war.

After the discovery of the Trench war machine and depending on the previous actions of your party and your players’ inclinations, you may want to focus adventures on one or more of the following:

  • Uncovering the dopplegangers influencing political decisions in nearby countries.
  • Sneaking into the Trench and taking out key leaders, such as the aboleth manipulators, or the key components required to enhance the aboleth’s telekinetic abilities.
  • Making a deal with the Elder Brain against the aboleth.
  • Making a deal with one or more ancient dragons, good and/or evil.
  • Going on a divine, multi-planar quest to recruit spiritual allies from the gods that defeated the aboleth.
  • Sealing allies from the adjoining countries
  • Once the truth behind the mine’s destruction is uncovered, the party may try to ally with the kraken whose country was devastated by the aboleth weapon.
  • Seek out allies within the githyanki or githzerai against the mind flayers. Though the gith races aren’t naturally aquatic, the magitech that allows them to sail and survive the Astral plane could easily be adapted to fascinating aquatic ships and breathing apparatuses.

Unless the party attempts to kill Vargorish directly at this level, the war machine will advance by the time they reach 15th level. Whether or not the army continues to have mind flayer allies, a weapon of mass destruction, or key sleeper agents among the surrounding countries will depend on the PCs’ actions.

16th-20th level

At this level, the aboleth army will be on the move. Vargorish will remain in the Trench using psychic and arcane power to oversea the horde, triggering sleeper-agent pawns at key moments to disrupt defending forces, unless the party has already uncovered them.

Some parties will likely want to sneak through Trench and confront Vargorish in his mountain fortress. If they can confront the livyathan and kill him, the invading army will loose two of its key advantages. 1) Vargorish’s psychic powers are strong enough to connect his generals mentally, coordinating attacks and making changes to battle plans faster than any normal army, and 2) any creatures under Vargorish’s personal domination powers will be freed, and likely wish to seek revenge on any of the beast’s lieutenants, throwing at least some of the horde into turmoil. This should necessarily stop the army en masse, but it will make it significantly easier to destroy if the party has gathered enough allies and helped create solid military strategies. Whether or not evil dragons, the kraken, Elder Brain, or other questionable allies turn on the “good” countries after is something for you to decide.

As I mentioned in the previous campaign outline, the classic 3.5 module, Red Hand of Doom, is an excellent source for creating a campaign or series of adventures based on an attacking horde, as well as running adventures during one or more sieges.

If you prefer an “urban” combat within the aquatic capital city, look to Red Hand of Doom and my own posts about our RHoD campaign for inspiration on ways to make large-scale combats feel more personal, and to help the PCs feel like their actions in the campaign (such as making new allies and uncovering threats) made a significant difference in the final battle.

Additional Resources




towering draconic form breaks the water’s surface with a bubbling roar. Its head possesses the jaws and spiky horns of a dragon and the three eyes of an aboleth. Its front limbs are great tentacles, and it lacks rear limbs, its body ending in a tentacle-like tail.

Gargantuan aberration-dragon, Lawful evil

Armor Class 22 (natural armor)
Hit Points 350 (21d20+126)
Speed 40 ft., swim 80ft., fly 80ft.
Initiative -1 (or +10 if using the alternate Initiative rules)


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

Saving Throws Dex +6 Con +13 Wis +10
Arcane +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 Aboleth, Common, Deep Speech, Draconic, Primordial
Challenge 21 


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


MultiattackVargorish can use his horror. He 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.
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.
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. Vargorish may create a telepathic link with a number of creatures he can see equal to his Intelligence score (26). These creatures are typically his field generals. Creatures included in battle mind may communicate telepathically with each other and Vargorish at any distance. Any creature included in battle mind has their proficiency bonus increased by 2 to a maximum of 7. As an action, Vargorish may perceive through the senses of one member of the the battle mind. Each link continues until dismissed by Vargorish, Vargorish dies or goes unconscious, or until he is on a different plane of existence than the member.
Each creature of Vargorish’s choice that is within 120 feet of him and aware of him 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 Vargorish’s Horror for the next 24 hours.
Acid Slime Breath (Recharge 5-6). Vargorish 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 gain the ability to breath only water (not air) for 3 hours. 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 (see below).
Enslave (3/Day). Vargorish targets one creature he can see within 60 feet of him. The target must succeed on a DC 23 Wisdom saving throw or be magically charmed until Vargorish dies or until he is on a different plane of existence from the target. The charmed target is under Vargorish’s control and can’t take reactions, and Vargorish 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 Vargorish.


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. Vargorish makes a Wisdom (Perception) check.
Tail Attack. Vargorish makes a tail attack.
Wing Attack (Costs 2 Actions). Vargorish 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.

On initiative count 20 (losing initiative ties), Vargorish 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 Vargorish 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 Vargorish sending powerful currents throughout the area. Each creature other than Vargorish 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 Vargorish 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.

The region containing an 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.

Swarm of Acid Jellyfish

Large swarm of tiny beasts

Armor Class 14 (natural)
Hit Points 40 (8d8)
Speed 20’; climb 20’; swim 20’
Initiative +1

Str 6 (-2) Dex 14 (+2) Con 10 (+0) Int 1 (-5) Wis 7 (-2) Cha 1 (-5)

Damage Resistances bludgeoning, piercing, slashing
Condition Immunities charmed, frightened, paralyzed, petrified, prone, restrained, stunned
Skills Perception +0
Senses Blindsight 10 ft., Passive Perception 8
Challenge 3 (700xp)

Water Breathing. The acid jellyfish swarm can breath water.

Swarm. The swarm fills a 10 foot by 10 foot square, can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Tiny beast. The swarm can’t regain hit points or gain temporary hit points.



Tentacles. +5 to hit, reach 0 feet, all targets in the swarm’s space, 10 (4d4) acid damage and the targets must make a DC 10 Constitution save. On a failed save, the target is overwhelmed by painful stingers, becoming poisoned for 1 minute. The target may repeat the save at the end of each of its turns to end the condition.