Cheap plastic imitation of the Amulet of Yendor
The cheap plastic imitation of the Amulet of Yendor is an amulet that exists solely to confuse you. It has a 50% chance of being generated on the Rogue level [1], a 50% chance of being in the inventory of a double-troubled Wizard of Yendor when you don't have the amulet (0% when you do) [2], and player monsters on the Astral plane all carry one [3] (that's why they're stuck there).
If the real Amulet is left in a bones file, it gets converted to a fake amulet when the file is loaded [4].
It has no effect when worn. It can be considered one of the most useless items, next to iron chains.
If not identified, the cheap plastic imitation can be told from the real Amulet of Yendor by trying to put it into a container: the real amulet will resist.