One of the exciting things about writing an aquatic setting is that there are whole creature types that don’t have a single aquatic or swimming creature in the Monster Manual, VGTM, or MTOF. Fiends, for instance. There have been aquatic fiends in D&D – the 3.5e Fiend Folio has four – but they’re rare. To get the obvious thing out of the way, you can just bolt a swimming speed, the amphibious quality, and some gills and fins onto existing fiends. In fact, I encourage you to do a bit of that. Those are still going to look like surface-dwellers that got a fresh coat of paint, though, so in this article I’m presenting a new demon and a new devil, purpose-built for undersea use.


A vitriseng is an aquatic demon that attacks unseen and leaves a strange transformation in its wake. They are naturally colorless and almost invisible; only while they are feeding and after they have recently fed do they gain color. The victims they leave behind are drained to transparency, with jellified flesh or chitin. Above all other prey, vitrisengs hunt the endlessly changing and colorful voda.

Vitrisengs prefer to hunt in vibrant places such as coral reefs, where everything they touch can feed them. The leaching of color and form can take years to recover, if there is anything left to recover at all. They are also often found in places where a battle has left corpses behind, as they can arrive even more swiftly than other aquatic scavengers. They are feared and hated by all aquatic peoples, and rumors of one can lead blood enemies to set aside differences to carry out a hunt.


Large fiend, chaotic evil

Armor Class  15
Hit Points 199 (21d10 + 84)
Speed 5 ft., swim 50 ft.
14 (+2) 20 (+5) 18 (+4) 10 (+0) 12 (+1) 17 (+3)
Skills Perception +5, Stealth +13
Damage Resistances cold, fire, lightning, radiant; bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities poison
Condition Immunities poisoned
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 15
Languages Abyssal, telepathy 60 ft.
Challenge 12 (8,400 XP)
Natural Transparency. The vitriseng’s flesh and bones are transparent when it has no undigested color in its system. It is constantly invisible until it reduces a creature’s maximum hit points, or it reduces a creature to 0 hit points. Once it becomes visible, it regains its natural invisibility once it goes at lest 1 hour without reducing a creature’s maximum hit points.

Keen Scent. The vitriseng has advantage on Wisdom (Perception) checks that rely on its sense of smell.

Prismatic Absorption. When the vitriseng is in the area of an illusion spell that creates visual effects, it gains 8 (1d10 + 3) temporary hit points, not more than once per spell. When it succeeds a saving throw against a prismatic spray or prismatic wall effect, it consumes and dispels the spell, gains 40 temporary hit points, and loses its Natural Transparency trait for 1 hour.

Aquatic. The vitriseng breathes water, not air. It can hold its breath for up to 1 hour at a time.


Multiattack. The vitriseng makes four attacks with its tendrils.

Tendril. Melee Weapon Attack: +9 to hit, reach 20 ft., one target. Hit: 16 (2d10 + 5) piercing damage plus 4 (1d8) poison damage. The target must succeed on a DC 16 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Guuldrom (Distortion Devil)

The guuldrom, or distortion devil, is an inquisitor among devil-kind, revealing weakness and treason against the authority of archdevils and Nemesis herself. They are precise and ruthless in their search, finding fault worth punishing in almost everyone they encounter. Though a guuldrom’s body is approximately humanoid, it has a featureless, mirror-like face with only a maw of jagged teeth. Its limbs end in webbed hands and feet, and its forearms and lower legs have fins. Guuldroms usually wield sharktooth blades or rapiers.

Guuldroms are feared and loathed by other fiends, as they carry authority above their station, infiltrate even powerful strongholds almost at will, and reveal secrets great and small. Even pit fiends would rarely summon or associate with a guuldrom, though guuldroms have no similar compunction to deputize lesser devils into service.


Medium fiend, lawful evil

Armor Class  17 (natural armor)
Hit Points 202 (27d8 + 81)
Speed 30 ft., swimming 50 ft.
12 (+3) 20 (+1) 16 (+2) 17 (+3) 14 (+2) 20 (+5)
Saving Throws Dexterity +10, Wisdom +7
Insight +7, Intimidation +10, Perception +7
Damage Resistances cold; bludgeoning, piercing, and slashing from nonmagical attacks not made with silvered weapons
Damage Immunities fire, poison
Condition Immunities poisoned
Senses darkvision 120 ft., passive Perception 17
Languages Infernal, Common
Challenge 14 (11,500 XP)
Infernal Inquisition. If the guuldrom observes a creature for at least 1 minute or hits with its bite attack, it can force the creature to roll a DC 18 Charisma saving throw. On a failure, the guuldrom learns the creature’s Ideal, Bond, and Flaw. A creature protected by protection from evil and good, magic circle, or mind blank automatically succeeds its saving throw against this effect.

Powerful Swimmer. The guuldrom can Dash as a bonus action while it is swimming.

Amphibious. The guuldrom can breathe both air and water.

Spectral Passage. As a bonus action, the guuldrom can become incorporeal until the start of its next turn. While incorporeal, it has resistance to all damage except force damage, and it can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Devil’s Sight. Magical darkness doesn’t impede the devil’s darkvision.

Magic Resistance. The devil has advantage on saving throws against spells and other magical effects.


Multiattack. The guuldrom makes four melee attacks: three with its sharktooth blade and one with its bite.

Sharktooth Blade. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 9 (1d8+5) piercing damage plus 13 (3d8) psychic damage.

Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 12 (2d6+5) piercing damage, and it can use its Infernal Inquisition trait.


The sharktooth blade is a new weapon found in Under the Seas of Vodari.

Sharktooth Blade. 25 gp, 1d8 slashing, 3 lb. Finesse, special
Special: While underwater and making a melee attack with a sharktooth blade, the attack roll does not have disadvantage, even if you don’t have a swimming speed.

Design Notes

It’s curiously difficult to make something feel fiendish, as distinct from “just another predator,” because – for OGL reasons – I can’t touch on the Nine Hells of Baator or the Infinite Layers of the Abyss. I’ve written new lore for devils and demons in Vodari, which will appear in Under the Seas of Vodari, which is where the Nemesis character is explained.

(If you’re one of the people reading this who also knows the Wildlands South campaign, I can neither confirm nor deny that I think Nemesis would wear silver eyeshadow.)