Deep One Hybrid

Deep One Hybrid CR 1/2

This fish-frog hybrid is of roughly humanoid shape with thick scales, claws, webbed extremities, and huge gill slits. Lidless bulging eyes and lipless fang-filled jaws shape its leering face.

XP 200
Deep one hybrid rogue 1
CE Medium humanoid (deep one, human)
Init +5; Senses low-light vision; Perception +5


AC 13, touch 11, flat-footed 12 (+2 armor, +1 Dex)
hp 12 (1d8+4)
Fort +3, Ref +3, Will +3
Weaknesses sea longing


Speed 20 ft.
Melee short sword +2 (1d6+2/19–20)
Special Attacks sneak attack +1d6


Str 14, Dex 12, Con 17, Int 10, Wis 13, Cha 8
Base Atk +0; CMB +2; CMD 13
Feats Improved Initiative, Iron Will
Skills Bluff +3, Disguise +3, Intimidate +3, Knowledge (local) +4, Perception +5, Sense Motive +5, Sleight of Hand +5, Stealth +5, Swim +10; Racial Modifiers +4 Swim
Languages Common
SQ final change, hold breath, trapfinding +1


Environment any coastal
Organization solitary, pair, or mob (3–16)
Treasure NPC gear (leather armor, short sword, other treasure)

A deep one is a repulsive amphibian hybrid with a vaguely humanoid form. They sometimes shamble upon two limbs, and sometimes four. They can leap or hop as well as walk or swim with natural grace.

Deep ones do not have a fixed size. When starved, they shrink to tiny size. When overfed, they can grow truly huge: 50-60 feet tall or more. The average deep one is a little larger than a human, weighing some 300 lbs., and standing around 7 feet tall if not for its normally hunched, almost crouched posture.

Deep ones are able to interbreed with any vertebrate being. The offspring look like the non-deep one parent, but over the years they gradually mutate to deep one form.

Humanoids are shaped much like deep ones (two arms, two legs, etc.), so the mutation process is comparatively short for them, requiring no more than a few decades. Less humanoid creatures, such as dolphins or alligators, may take longer. of course, the deep ones can also spawn amongst their own kind. Deep ones’ offspring ultimately combine aspects of both parents.

Conquest through Breeding

To some, the deep ones’ ability to breed with any creature implies they are not necessarily from the sea (or, at least, don’t have to permanently be sea dwellers). It occasionally happens that a group of deep ones break away from the normal sea habitat and live in a freshwater environment, or even become wholly terrestrial for a time. They can crossbreed with elves, orcs, or even less savory creatures, and their dark culture can infest any land.

When a deep one mates with a non-deep one creature, the offspring initially appears to be a typical specimen of the non-deep one parent. Typically, such children are raised in secrecy away from society so that they can grow up and complete their change.

In some cases, particularly those involving children who are orphaned at young age, deep one young grow up with no knowledge of their true nature until the change occurs. It has happened more than once that a group of well-meaning do-gooders has swept into a port village, wiped out a band of cultists, and rescued infants and children, only for those youths to become monstrous over time and renew the cult’s activities.

The change itself is gradual, taking place over the course of decades. As it progresses, the hybrid grows more and more ichthyic in feature: hair progressively falls out, eyes grow large and protrusive, webbing begins to grow between fingers or toes, scaly patches appear on the skin, or thick deep wrinkles or folds of skin manifest on the flesh. As the change progresses and the hybrid ages further, these physical changes increase. Heads change to become unnaturally elliptical in shape, lips widen and grow short fleshy tendrils or feelers along the edges, teeth grow sharp and perhaps serrated, and skin grows dry and painful when not frequently exposed to water. Those who suffer from this affliction find it increasingly painful to walk, and do so with a stumbling or shuffling gait.

Section 15: Copyright Notice

Sandy Petersen’s Cthulhu Mythos, © 2017, Petersen Games; Authors: Sandy Petersen, Arthur Petersen, Ian Starcher.

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