6 Aquatic Encounter Seeds for 6th-10th Level Characters

In this series I will be 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 week I bring you aquatic encounter ideas for parties of 6th through 10th level characters. You can find lists of the villains, lieutenants, and minions referred to in the associated Enemies 6th-10th level post.

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


Undead Villains

Unlike surface cultures, aquatic races rarely bury their dead in the ground. Civilized races that gather in large underwater cities sometimes create necropolises from coral reefs and atolls, ritually weigh down bodies to drop into drenches or the Deep, or wrap bodies in organic cocoons and float them in seaweed forests until they decay. Though the first and last options create versions of graveyards that can be manipulated by negative energy the same as surface graveyards do, crevices on the edge of large settlements or trenches that have been used by nomadic cultures for hundreds if not thousands of years to bury dead provide a dangerous amount of material for necromancers and aberrations from the deep.

Though there are no undead directly on the list, it is easy to create a mid-level undead spell caster by using the Archmage NPC and adding the following abilities. Also, increase the CR of the archmage by 1 if you use these options:

Damage Resistances piercing and slashing (from non-magical weapons), psychic
Damage Immunities cold, necrotic, poison
Condition Immunities charmed, exhaustion, frightened, paralyzed, poisoned, stunned
Vulnerabilities bludgeoning (from magical weapons only)
Senses Darkvision 60’

Drink Death. When a creature within 30 ft of the undead archmage is reduced to 0 hit points, the mage can use its reaction to heal 20 (4d10) hit points.
Empower Undead. All undead allies within 30’ of the lich cleric are affected as if by a bless spell.
Unnerving Gaze (recharge 5-6). As a bonus action, the undead archmage can force all living creatures within 30 feet to make a DC 17 Wisdom save or become frightened for 1 minute. The creatures can make an additional save at the end of each of their rounds to negate the effect.

Undead Story Seeds

  • An undead archmage has had numerous undead minions shipped into and planted around the PCs’ city. Skeletons are packed in containers. Wights are folded into barrels. Wraiths are bound to jars and other mundane containers. These sleeper agents have been made inactive by a diadem they wear that also links them to their master. At midnight of the full moon, the army of agents will awaken around the city, creating havoc and distracting the city’s guards while the archmage and several orca-shaped flesh golems infiltrate the temple of a deep sea god to retrieve an evil artifact held there under the clerics’ protection.

Aberration Villains


Though one of the most iconic villains of D&D, aboleth are rarely used to their full potential. Cthulhu-like horrors from the deep, aboleth have vaunted positions in the history of many campaign settings. Pathfinder’s Golarion tells tales of the aboleth empire going to war with the ancient human Azlanti, for example.

Their introduction in the 5th ed Monster Manual says it all:

“Before the coming of the gods, aboleths lurked in primordial oceans and underground lakes. They reached out with their minds and seized control of the burgeoning life-forms of the mortal realm, making those creatures their slaves. Their dominance made them like gods. Then the true gods appeared, smashing the aboleths’ empire and freeing their slaves.”

Though much is made of the aboleth’s numerous slaves, the largest members of their armies were a race of mutated humanoids called the ulat-kini, commonly known as skum [see the Enemies post for both a monstrous stat block and a playable PC race of ulat-kini].

The core aboleth presented in the various Monster Manuals is an impressive creature, but if you are looking for even more options for these ancient and terrifying creatures, check out Rogue Genius GamesMonster Menagerie “Horrors of the Aboleth”.

Aberration Story Seeds

  • The aboleth empire has long since crumbled, but the survivors of that ancient time did not die, they retreated to the depths of the Trench. The Trench refers to both a labyrinthine series of miles-deep gashes in the ocean floor, as well as the aboleth city that has thrived there over the centuries. The aboleth lords have a new leader and the creature has stirred the alien civilization into rebuilding their empire, both beneath the waves and along the surface coasts. Powerful ulat-kini (aka: skum to other races) still in service to the Trench lords have poured from the ancient metropolis to summon their brothers from across the globe. Aboleth psi-sorcerers pool their telekinetic powers to shatter coastal fault lines, tearing populations of surface dwellers into he sea. The life-and-death struggle triggers ancient potential for water breathing and revealing among them those whose ancestors once served the aboleth.

Monstrous Villains

Aquatic yuan-ti combine the appearance of sea snakes with that of merfolk, but otherwise have a similar history of serpentine worship and transformation. The yuan-ti and naga are the players in a centuries-old series of skirmishes that, at times, explode into war.

Per their entry in the Monster Manual: “Spirit nagas live in gloom and spitefulness, constantly plotting vengeance against creatures that have wronged them- or that they believe have wronged them. Lairing in dismal caverns and ruins, they devote their time to developing new spells and enslaving the mortals with which they surround themselves. A spirit naga likes to charm its foes, drawing them close so that it can sink its poisonous fangs into their flesh.”

Monstrous Story Seeds

  • A decade ago, the spirit naga, Ishka, had done what other naga had seemed impossible—it had placed itself at the head of a temple of yuan-ti as their spiritual leader. The unholy alliance nearly destroyed two adjoining merfolk kingdoms before a party of adventurers convinced the yuan-ti to rebel. Ishka, murdered by its followers, was subjected to a twisted form of the ritual yuan-ti use to create bone naga, but the ritual failed. Instead of turning it into a servant of the yuan-ti, Ishka’s rebirth instead too nearly 10 years to complete. Its body is now a twisted abomination of its former glory and now possesses the power to create and control the dead, which it plans to use for revenge. The PC’s home town may be caught in the conflict, the temple (or even Ishka) may approach the PCs for assistance against their common enemy, or the PCs may uncover the naga’s twisted plan to summon or create an army of ghouls, ghasts, and flesh golems that will threaten civilization.

Elemental Villains

Marids are a type of genie that hails from the elemental plane of water. They are arrogant, boisterous, tellers of tall tales (typically involving themselves or their ancestors). It is extremely rare for a marid not to claim some form of royal title as they hold themselves above all creatures, including other genie. Marid are known for their elaborate mansions, filled with slaves of the highest quality (that they care very little about outside of their ability to grant status).

Elemental Story Seeds

  • The PCs attend the performance of, and/or know personally, one of the most popular and stunning singers in the region. The performer may be in a small town working their way to stardom, or already well known and living in a metropolis. The singer can be of any standard race and of either sex, though merfolk and selkies work well (as would cetes, a sentient and civilized race of marine mammals upcoming to From the Depths). After the performance, 4 water-elemental invisible stalkers in the service of a marid abduct the singer and escape through a natural portal to the elemental plane of water located in a deep sea trench. The singer, if not adapted to the pressure and cold, will be protected by magic, as well as given the ability to breath water if from a breath-holding race. The PCs must find a way to reach the portal (if they aren’t adapted to that depth), track the kidnappers to the marid’s lands, and rescue them from slavery.

Humanoid/Piscinoid Villains

The archmage humanoid NPC in the back of the Monster Manual is an excellent template for any humanoid race. With a few tweaks to its spell list or special abilities, the archemage can be an archetypal necromancer, a summoner tied to the elemental planes of earth or water, or a powerful illusionist looking to rule through misdirection and fear.

Humanoid/Piscinoid Story Seed

  • The kingdom the PCs are currently in (perhaps even their home kingdom) has some questionable laws regarding cecaelia that rarely come into effect because of the races’ rarity in the area. The PCs discover an underground trade in cecaelia slaves, a cecaelia PC is arrested and charged without trial, or some other event uncovers the prejudice inherent in the system. When a powerful cecaelia illusionist decides to avenge the horrors inflicted behind the scenes on his/her people, the PCs must decide whether or not to join the cause, negotiate a change, or shut the murderous spell caster down.

Giant and Dragon Villains

In many campaign worlds, and in the material provided in the 5th edition Monster Manual, the giants once ruled the planet through brutal wars with the dragons. Behirs are said to have been created by the giants as both pets and weapons against the giants’ hated foes. Though storm giants are chaotic good by nature, that does not mean that 1) a good creature can’t be an antagonist and 2) that the nature of an individual might override the racial tendency.

Giant/Dragon Story Seed

  • A storm giant of venerable age and questionable moral character has been in isolation in the ocean’s depths for centuries. Perhaps he or she is old enough to remember the giants’ time of glory, or perhaps it has spent its lonely days using magic to see into the past to sate its obsession with “better days”. Whatever the reason, this giant has decided to renew the war against the dragons.Whether on a local or global scale, the giant has either summoned or created scores of aquatic behirs and collected an army of fanatics (scrags, sahuagin, merrow) as well as koalinth mercenaries. Perhaps an aquatic dragon comes to the PCs for help (making it a black or green would be even more intriguing), or maybe the war has been brewing behind the scenes for months and the PCs’ home town is caught in the middle.

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Rich Howard's obsession with gaming started 35 years ago when his older brother finally let him invade his AD&D game. Since his first sleep spell, Rich has wandered the world of roleplaying, board and computer games as fascinated with their potential to teach and inspire as to entertain.