Witch Coins are cursed gold coins, given by witches to misers, enemies, and those who they seek to teach a lesson. They look much the same as normal coins, although often close inspection will reveal the witch's profile in place of the ruler or monarch they were minted under.
Every night, witch coins split all other money in their container into its value in a lower denomination. Gold coins split into silver, silver splits into copper, and copper splits into lead slugs.
The sheer volume of coins created this way is usually enough to explode coin pouches, burst open chests and safes, and cause a whole bunch of transport problems due to weight and volume.
No value is actually lost unless they turn to lead, in which case they might maybe be able to be used or sold as sling bullets.
Anything purchased with a Witch Coin will invariably have problems with workmanship and quality, even if it looks fine on the surface.
The curse can be broken via Remove Curse, or by giving the coins away.