Agony, also known as Liquid Pain, is exactly what it claims to be: the distillation of pain and suffering by magical means into a drug. The resulting substance is a thick, reddish liquid resembling blood only more viscous.
It is highly prized among certain extra-planar beings, who can use it to feel pleasures greater than they are otherwise able. Side effects of Agony include an initial stunning effect that incapacitates the user for a brief period and leaves them groggy for a time after that. Curiously, it also makes them more attractive to anyone around them for a period lasting anywhere from one to eight hours.
Agony would likely be a drug of great addiction among demons, devils and their ilk, were it not for the fact that an overdose causes unconsciousness, which means that the effects are wasted instead of the users.