Forged by the death of the second Daemon Lord the Stygian Knife was originally little more than a decorative knife that wasn’t all that sharp along it’s edge but did possess a point. Not even a hand span in size from hilt to point.
When holding the Stygian Knife the weilder is completely undetectable by any and all means. Strangly the utility of the Stygian Knife does not grow with the weilders experiences but with it’s own experiences. As such those looking for the weilder of the Stygian Knife may be able to find them provided they are creative enough to use a method that the Stygian Knife as not yet encountered. The time for which the weilder remains exposed depending on the weilders pratice with this function but once the method has been used to find the weilder has been negated it will never work again. Regardless of weilder current or future.
The limits of what the Stygian Knife can hide, alongside how, much alike all artifacts is completely unknown. However it is thought that with enough experience the Stygian Knife may be able to hide it’s weilder from death itself.