Named after the Roman shades of dead, lemures are the protoplasmic building blocks of devilkind. As such they demonstrate the peril—and potential—of evil. If villains (or characters) are lawful evil in life, existence as a lemure is what awaits them once eons of torture have expiated their sins and stripped the memories from their souls. And even pit fiends fear failing in their duties and being reduced to this primordial status. On the other hand, Hell is the multiverse’s ultimate meritocracy—and once one is a lemure, there is nowhere to go but up…
On a more practical level, lemures’ low CR and low summoning cost make them an easy way to get PCs fighting the powers and politics of Hell as early as first level.
Not everyone seeks out adventure; sometimes it finds you. A freak alignment of the planes carries the village square to the first layer of Hell for a horrific ten minutes. The village youths must join the militia in warding off a mob of lemurs. After the battle, their innocence lost, the youths begin their career as adventurers to root out what happened—and why.
In the devil-worshiping kingdom of Dis Proxima, lemure duels and ichorsports are a popular entertainment for the well heeled. These acts of summoning of course raise the spellcasters’ risks of one day becoming creatures themselves…but the proud Proximans insist that they are the masters of Hell, in this life and the next, and need not fear such a fate.
An extortion racket has a stranglehold on the Wharf District. A letter borne by a dead man (reanimated as a zombie and sent directly to the Wharf Watch) fingers a novice group of inquisitors and detectives. They must clear their names before the Watch finds them, as well as handle the hired thugs, sewer amoebas, and familiar-kidnapping swamp goblins the investigation throws their way. Eventually, they uncover the mastermind of the plot—a crime boss whose greed morphs him into a lemure before their very eyes.
—Pathfinder Bestiary 79