I like the lamhigyn. First off, I just like finding out about things that live in the Abyss that aren’t demons. I like the greater ecology it suggests, and it’s thematically appropriate that even demons don’t have a lock on this chaotic plane.
Second, with their squat bodies and three eyes and general misbegotten appearance, there’s a cheesy Saturday morning cartoon/afternoon movie quality to lamhigyns. That’s supported by both their mechanics—their ability to wrap their wings around their victims’ faces to blind them is the kind of move that would have been achieved through practical effects and puppetry in the ’80s—and their descriptive text—with the suggestion that canny PCs could trick a whole hive of lamhigyns into tearing themselves apart, just like a plucky B-movie protagonist in dire straits.
That doesn’t mean lamhigyns aren’t deadly…and in fact that best time to send lamhigyns against the PCs is a) when they’re trying to do something sneaky and shouldn’t be fighting, or b) when they're already worn out and low on resources. A CR 3 lamhigyn looks a lot scarier when it has 29 friends and a battle will draw other Abyssal residents your way.
A hive of lamhigyns guards a narrow ford near the border of the Abyss. Ostensibly, the squat outsiders offer a riddle challenge, but since they only speak Abyssal and the “riddles” are rudimentary at best (“What did the lassst man we ate have in hisss pocketsss?”) the challenge is essentially the lamhigyn equivalent of drawing straws to see who gets to dine first. If adventurers can convince one of their interrogators that they’ve prearranged a deal with another lamhigyn, the whole clutch will fall upon each other in fits of outrage and envy.
The shortest distance from a wizard’s tower to a sealed bank vault is an otherworldly path that at one point travels through the intestines of a giant Abyssal beast. Fortunately the creature’s digestive tract is so engorged and slow-acting that adventurers have little to fear (treat as nonlethal damage). But years ago a clutch of lamhigyns took up residence in these dank bowels, and they view live adventurers as a welcome change of menu.
The Abyss births species in unusual ways. Most lamhigyns are found in ponds and marshes, having hatched from jellied spawn in the manner of frogs. But some travelers have reported lamhigyns hatching from flying cysts, eating their way out of decaying bile whales, slowly pupating in membranous walls of tissue, and growing in gourd-like bean pods amid the branches of weeping willow trees that actually weep.
—Pathfinder Bestiary 5 154
Notice that lamhigyns are Int 5 and speak Abyssal…because in the Abyss, not only does everything want to eat you, but they’ll also talk about that fact incessantly.
It should be noted that the Llamhigyn Y Dwr is a Welsh creature—kind of a bat-armed frog with a stinging tail. I didn’t reference it above because the Paizo version is pretty divorced from the source material. But if you’re looking to beef up the encounter list for your fantasy Wales, it’s actually a pretty easy tweak: Change its language to Sylvan and its environment to “any rivers or marshes” and you’re good.
(Most likely the legend of the Welsh Llamhigyn Y Dwr came about after an encounter with a stingray. If that seems unlikely, well…oceans are weird. A friend of mine once got his picture in the paper when he found a Southeast Asian nautilus on the beach after a storm…which would have been reasonably impressive in, say, California. We were in Massachusetts.)
PS: Anyone Welsh want to teach us how to say “Lamhigyn”?