I am the Holder of Shadows. You ought never meet me, so pray that that ounce of mercy has been granted you, Seeker.
In any city, in any country, on a Thursday, head to any open park area you can get yourself to. It is suggested you bring along a firearm or other weapon you can use to easily end your own life, as this is preferable to any fate you may find during my task.
Ask the first person you see where "The Holder of Shadows" is. No matter where you are, or where you live, or what temperature it is, it will begin to snow. Do not allow yourself to be touched by this snow or you will be frozen for eternity, a silent sentinel of ice and flesh, never again to feel the warmth of the sun.
When the snow ceases, you must run. Run as quickly as your legs will take you, for they will follow. Get to the nearest residential house you can find, and knock on the door exactly three times. If nobody answers, or you knock too many times, close your eyes and pray that your death will be painless - though it very likely won't be.
When you enter, there will be a single light in the center of the room, suspended in the air. Although it has no physical form, striking it will destroy it. You must do so, or else the shadows cast by objects in this light will take corporeal form and attack. Act quickly - if you tarry your chances of survival will be... small.
When the light is destroyed, the entire house will be cast into pitch-black darkness. Only the door you entered through will allow any light into the room. Do not attempt to exit this way, or even look outside, for my beasts are still waiting, ever patient. Instead, you must find the basement and descend into it. If you were unfortunate enough to choose a house with no basement, you will have to look somewhat harder.
Do not show any sign of fear or doubt, or you will find yourself lost in the darkness. The basement will be lit normally. If the objects in the basement cast shadows, then you will survive. If they don't, commit suicide as quickly as possible. It will be painless compared to what my minions will do to you.
If shadows are cast, look for the nearest bladed or blunt objects you can find and use as a weapon. As soon as you pick it up, shadows will vanish from the other items in the room, one by one. Close your eyes as tightly as possible, turn around, and swing your weapon. It will feel as if your hand passes through water, and with the parting of the viscous material will come an unearthly scream, a scream beyond any reasoning or comprehension. Open your eyes. The shadow beast will drop to the ground, then dissolve. The weapon you hold will slowly grow hotter, then burning, then red-hot, then white-hot. If you do not let it go, the fire will consume you and you will burn for an eternity, and the eternity beyond that. When you drop it, it will burn through the earth itself. Ignore the hole and grab the crystal at your feet.
The crystal will be ebony black in color, and fit snugly into your palm. As long as you hold it, the shadows will not envelop you, and you will see through any natural darkness.
This crystal is Object 173 of 2538, my gift to the Seeker who has earned it.