Assassin's Eye: A Wondrous Item for 5e
Everything has a weakness, but it’s often hard to see. With this glass eye forged by unscrupulous glassblowers and enchanted by hidden societies dedicated to death you can find any creature’s fatal flaw at a glance.
Assassin’s Eye
Wondrous item, rare
The sickly green iris of this expertly crafted eye resembles a whorl of thick poison that refuses to dissolve. Its pupil is a bare skull. With the assassin’s eye you can size up a creature as a bonus action. You learn any damage vulnerabilities the creature possesses. If the creature possesses any damage immunities you learn what kind of attacks bypass those immunities, if any. If the creature possesses regeneration you learn what damage types suppress its regeneration. If the creature possesses any resistances, immunities, or other damage-reducing abilities granted by magic items you learn where these items are carried or worn on the creature’s person. An assassin’s eye requires attunement.
An assassin’s eye does not take up a standard item slot. To attune to the eye you must be missing an eye and wear the assassin’s eye in the empty socket. Once attuned the assassin’s eye functions as a normal, sighted eye.