From Introduction:
It pools inside cracks in the earth, deep within caves where there is no light. It can be seen forming worm-like tendrils, or evaporating into the air like vapour. When the light hits it just right, it glows an unnatural greenish hue. Beware this arcane fluid, for it is no ordinary alchemical! It will infect you, burrowing into your wounds and from thence into your soul.
It is through this fluid that the maligned sorcerers of our day summon the Purple Man. They cannot call the fiend up from the pits of Hell without a sacrifice, of course, but such is their villainy, these warlocks, that they lead their chosen victim into darkness to face the foul fluid alone and unprotected. Once claimed, they serve as a vessel for this violet-hued demoniac, their own soul lost to the heavens, cursed to wander fruitlessly and lamenting.
Do they even know how long they have, once the doom is upon them? I have seen it claim more than one brave and lawful adventurer in my time as well. They go to fight the hordes of chaos, but forget to tend to their own wounds, and then the mark of purple is seen upon them. Only the bravest self-immolate to spare their comrades the horror they know is to come. The others — they flinch, they stall for time, they hope in vain for a cure.
And then they become the Purple Man. There might be only one this time, or many. But they are all the same creature inside, for the Purple Man dwells inside the Abyss, and these horrific bodies are merely his fingertips, probing into our world. Take it from me, for I am a wizard, and I have studied these matters!