Black fruit is a magical plant said to grow only in areas where nature has been corrupted by the dark arts. Some speculate that it occurs spontaneously, or perhaps that it propagates its seeds via extraplanar means in a twisted mockery of natural processes. However it takes root, the plant seems to draw nourishment from death, eventually bearing the vile black fruit for which it is named.
A piece of black fruit appears to be a roughly apple- or pear-shaped pome with a jet black exterior and a seedless, dark purple mesocarp. And while the fruit is fragrant and sweet, it is deadly if eaten. Most who ingest the tiniest piece of raw fruit die instantly.
The true horror of the black fruit, however, lies in its aftereffects. A creature who dies by ingesting it rises several hours later as a zombie. Such zombies are easily recognized from the purple-black ooze ringing their mouths. Because the merest amount of black fruit can achieve this effect, stories exist of whole gatherings or even entire villages dying and rising as undead in a single night after eating a communal meal tainted by it.
Such a potent substance has found other uses, of course, particularly in the hands of necromancers. The black fruit acts as one of the key ingredients necessary for achieving lichdom, and can be used to enhance many other forms of undead creation. It is so potent, in fact, that, for many applications, only a passing knowledge of the dark arts is necessary to achieve results.