Black Seer's Skull

"It's a powerful relic... if you don't mind the side effects." - Charnago Sarnazerrus on the risks of the Black Seer's Skull.

At a Glance
A potent relic of shadow energy, the Black Seer's Skull was a divination orb that allowed individuals to peer into the Astral Realm of The Shadowfell (but unable to communicate beyond these visions). The origins of the artifact remain a mystery but its texture implies it was at one time a real skull before being transformed into a scrying tool. In addition to its viewing properties, the Black Seer's Skull allowed a wielder to freely transport themselves between the mortal plane and The Shadowfell, at a cost. In exchange for a sliver of the wielder's soul, the Black Seer's Skull would envelop them in tendrils of purple magic, transforming them and the skull from one realm to the other.

Consequences
The Black Seer's Skull had long been sought after by individuals attempting to speak with deceased lovers or ancient warriors. The consequences of using the Black Seer's Skull to transport between the mortal and astral plane were, to put it mildly, damning. Use of the Black Seer's Skull would tear a sliver of the wielder's soul to feed the ritual, the result of which being:
 * Wielders who've had a sliver of their soul stolen would find themselves the target of wights, spirits, ghosts, and spectres who would sense the emptiness in the individual and attempt to possess them. These apparations would typically come in the twilight hours, making it difficult to gain a good night's rest.
 * Use of the Black Seer's Skull would reduce the clarity of one of the wielder's senses (taste, touch, smell, sight, or hearing). These effects would vary by use, but the reduction in any would lessen the wielder's perceptive abilities.
 * Continued use of the Black Seer's Skull to travel between realms would result in the wielder becoming a husk of their former self -- unemotional, sluggish, unable to feel, and developing chalky-white skin. They would also become increasingly hostile against other individuals.