The karkinoi are crab monsters. Specifically, humanoid crab monsters. That’s really all you need to know. Compelling societies, complex motivations, dark racial secrets? Nope, nope, and nope. (Okay, maaaaybe they were created by aboleths. Whatever.) It doesn't matter. They are CRAB. MONSTERS.
Which is not to say there aren’t some nice touches in the karkinoi stat block. The fact that they can scuttle sideways is a really cute touch. And I love that they have one massive claw, as if they were male fiddler crabs or Clawful from the Masters of the Universe toy line. For best results, send lots of them against low-level PCs, so their numbers and devastating claws give your players a good scare before they (hopefully) rally and outsmart these hulking crustaceans.
For dwarves, burial is mandatory. They believe a dwarf who is not returned to the earth in body is doomed to wander it in spirit. When a dwarven thane falls to a karkinoi raiding party while he is visiting coastal allies, his kin demand that adventurers are sent to retrieve his corpse. This means finding the karkinoi nesting grounds and facing down karkinoi nursery guards and swarms of already-hatched hungry karkinoi spawn.
A monastery sits perched like a seagull’s nest on a cliff face. An adventuring party’s reception there is cold, even hostile, from the first instant—the lawful evil monks do not welcome visitors or their soft lifestyles. But then karkinoi scale the cliff face in a mad attempt to devour or abduct everyone inside, and the adventurers are forced to work with the monks who were plotting to kill them only hours before.
Adventurers come across a bizarre sight: a massive whale, larger than any they have ever seen, beached on shore. The ivory from the bones alone might be worth a fortune, not to mention the price they might fetch from a naturalist for the scientific value. Coming around the side of the whale reveals that karkinoi are already hard at work dismembering the beast. They attack all intruders. Complicating matters is the rising sun. If combat is not resolved by noon (or if a fireball is cast in the vicinity), gases in the whale ignite, causing the corpse to rupture with the force of an explosion and release a beaching of globsters.
—Pathfinder Bestiary 4 173
I’ve seen a reference or two to karkinoi coming from Greek history/mythology, but details are super sketchy.
Though it’s still in my to-read pile, the module Plunder & Peril has stats for the karkinoi brood swarm.
Louise Glück may have been the big-name poet at my college, but my professor was Lawrence Raab, who made it into the Norton Anthology with “Attack of the Crab Monsters”:
So now you know
what I never found the time to say.
Sweetheart, put down your flamethrower.
You know I always loved you.
Oh, one final note: I know most of you come for the monsters, but I did get this really nice note:
Patch, I'm an irregular, but I just listened to last week’s [show] and you killed it! Lots of good, weird stuff—what is the post-CD equivalent of advance review discs? That Passion Pit track is good enough to be a highlight for a day of radio listening, but hearing it on your show I was tempted to fast forward.
Ed made my week with that note. And you would make my week if you listened, too. The file is good till midnight tomorrow night—download it and enjoy!