Yurian
"A Monster Emerges - 'Crab-man' Concept" © Marcus Whinney, accessed at his ArtStation here.
[My first D&D monster book was the AD&D 2e Monstrous Manual, so I always thought of the crabman as a "core" D&D monster. It first appeared in the AD&D 1e Fiend Folio, in which the artist didn't get the memo about them looking like nine foot tall crabs, and instead they appear to be six foot tall Great Gonzos with pinchers. These OG crabmen apparently also have a major interest in human women, although again, that's not in the text so is probably a preoccupation of the artist instead:
The name "yurian" comes from the 3rd edition Fiend Folio, the last time crabmen appeared in a physical D&D monster book. Crab folk do show up in the PDF-only 5e Mordenkainen's Fiendish Folio, where they are, in typical 5e fashion, attributed to the magic of hags instead of being a naturally occurring creature. They also appear in the 3.x and PF1e Tome of Horrors, and from there have migrated into Swords and Wizardry and other OSR-style games.
None of these crabmen have been particularly mechanically interesting. And in Pathfinder, their role has been co-opted by an expy, the karkinoi, which is genuinely evil and hungry for human flesh so your parties don't have to feel bad about killing them. However, this leaves the niche of weaker, neutral crab people open, and thinking about actual crabs (and borrowing from the karkinoi) gave me something for them to do besides make claw attacks.
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Yurian CR 2 N Monstrous Humanoid This giant humanoid has a head like a crab and a reddish-brown exoskeleton. It has two sets of arms, one of which is large and tipped with pincers, the other of which is smaller and ends in human-like hands.
Yurians are often called “crabmen” or “crab people” by outsiders, as they are indeed humanoid crabs. They are kin to the karkinoi, and some sages hypothesize that they are the base stock from which aboleth fleshwarping created those stronger monsters. Yurians are more peaceful than karkinoi, and live lives as beachcombers in coastal caves above or below the waterline. Yurians rear shellfish for food, supplementing their diet with seaweed, coastal plants and meat, and their material culture primarily consists of woodcraft and aquaculture. Yurians rarely use melee weapons, trusting instead to their claws, but may carry javelins for hunting on land and for defense.
There is little sexual dimorphism among yurians, but females are slightly larger than males, the better to make and lay vast amounts of eggs. Yurians lay eggs into open water near their settlements, and the hundreds of larvae resemble oversized plankton for the first six months of their life. In the planktonic stage, juvenile yurians fend for themselves, and many of them are eaten by predators. After about six months, a planktonic yurian molts into a form closely resembling the adult but at a quarter the size—these are capable of moving onto land and joining a consortium. It takes a juvenile yurian another several molts and about a year’s time before reaching adult size, and another year before sexual maturity. Yurians live fast and die young—few adults survive to more than 25 years of age.
Yurians are typically isolationist, thinking of most land-dwelling humanoids as inconsiderate pillagers of the sea and of sea-dwelling humanoids as competition or predators. Indeed, sahuagin find yurians delicious, and will gleefully exterminate a yurian consortium in an orgy of feasting if they locate one. When a yurian is critically injured, it can shed one of its claws in order to minimize the damage it takes and then flee; in areas where yurians commonly conflict with their neighbors, up to half of all members of a consortium may be missing a limb. The yurians can grow new claws when they molt, but this process takes weeks to accomplish. If yurians are able to come to an agreement with other cultures, they may trade wooden items and pearls for rare foods and silver. Yurians love the shine of silver, and keep their silver reserves well guarded above water to slow it tarnishing.
