Source: Bestiary, pg(s). 76
The tiny quasit has a thin, wiry body, curling ram-like horns, and wings. A typical specimen is 18 inches in height and 8 pounds in weight.1
Habitat & Society
Unlike most demons, quasits are not formed in the Abyss from the souls of dead mortals. Instead, it is created when an evil spellcaster seeks one as a familiar. The Abyss answers the request by forming a quasit linked to the spellcaster, which then appears directly on the Material Plane.2
Quasits serving as familiars have no society of their own, and serve at the whim of their masters. When the master dies, the quasit has the opportunity to try and seize its master's soul, transform it into a larvae, and take it to the Abyss. The quasit can then try to barter the larvae as the first step on the quasit's endless quest for advancement in the demonic ranks.
"Free" quasits may sometimes be found in flocks of up to a dozen individuals.1
The quasit is possibly the weakest of the demons, but it is a versatile creature. It can fight with its small claws and teeth, and its claws are poisonous. It can also transform itself into a bat, centipede, toad or wolf, and make itself invisible at will.
Perhaps its most useful ability, at least for the master of a quasit familiar, is that it can ask six questions each week to the fiendish powers. Of course, the correct answer is not guaranteed; even the Abyss does not know everything.1
Quasit familiars can be found in Golarion wherever there are reckless and unscrupulous spellcasters willing to risk trafficking with demons.
"Free" quasits are usually encountered in the Abyss.1 However, those who fail to capture their master's soul are forced to remain on the Material Plane;2 and sometimes they may even choose to remain there. In such cases they delight in tormenting mortals, so are typically found in urban areas where there are more targets to choose from.1