Soulfire Coin

The Soulfire Coin was an experiment by the Soulfire Wights to create a more powerful soul coin, which is used as currrency in the abyssal realms of demons and devils. These coins normally imprison only evil souls, and only one at a time - these coins can only be minted by a powerful dmeon lord deep in the nine hells. The Soulfire Coin however, can imprison multiple souls, and the souls need not be evil.

It is unknown how the Soulfire Wights created such a thing, but it seems they have only done so once - and shortly after its disastrous first use they miscalculated the cost and lost the coin.