The Black Cube Nickel is a federally recognized unit of currency with a face value of 5 cents. It weighs 4 ounces, measures 2 inches on an edge, is made of 100% black aluminum and engraved on 5 of the six sides with Jefferson's profile, the Monticello, and the requisite United States mottos, phrases, date, and mintmark.
The sixth side is missing, allowing exactly 20 'regular' nickels to fit inside a specially-shaped hollow cavity.
Unfortunately, besides it being unique, the Black Cube Nickel is endowed with a mysterious and powerful ancient and foul curse which bestows incredibly bad luck on its owner. Negative effects that have afflicted owners include depression, weakness, loss of appetite, intoxication, memory loss, foul body odor, blindness, physical mutation, rotting flesh disease, arterio-venous malformation, being visited by cyberdemons, and death.
