The Mirror of Ruinous Disrepute
This magical mirror covers most of a 20' long wall. It is covered with a lavish curtain suspended on a rod.
At first opportunity, reflections of persons in the mirror will step out and immediately go about ruining their original's life. They have all the abilities of their original, except that they are faster and more nimble. They also know their way around their dungeon of origin, as well as whatever their original knows at the time of duplication. First the reflections will set about having their originals killed. In a dungeon, this means setting off as many alarms, alerting as many guards, and offending as many potentially friendly NPCs as possible. They can predict the moves of their originals and have a 3-in-6 chance of being one step ahead when the party decides to get the hell out of this crazy dungeon.
After leaving the dungeon, the duplicates will set about ruining their original's reputation and legacy. Once they are satisfied that no intelligent being can remember the party without feeling nauseated, they will happily wink out of existence.
The reflections are made for self-preservation and will avoid armed confrontation, although they will fight cleverly should the need arise. They will will avoid being seen anywhere near their originals at all costs.
The reflections may be dispelled at any time by destroying the mirror.
The curtain covering the mirror is made of a rich, deep purple fabric. Embroidered in gold thread and other luxuriant materials are images of happy couples frolicking in a field. Upon closer inspection, the couples are always composed of two identical persons, and their expressions betray barely-concealed hatred. The craftsmanship of the object is exquisite and the curtain can be sold for 2000 gp to one who can afford it.
If you are especially mean, the curtain's opulence is actually an illusion. The effect is dispelled when the curtain is removed from the dungeon, revealing that it is actually but an enormous, tattered rag whose threads barely hold it together, for which no one would pay even a copper. The illusion is tactile as well as visual, but an attentive PC may hear the fabric tearing and fraying as they manipulate the curtain.