The Shadowstone, a black opal, was entrusted to the Menehune of Hawai'i. It has the power to absorb and transform Banality and increases the holder's ability to act "in the shadows," for example by stealth or in darkness. When used by those who understand the true interplay between Banality and Glamour, the gem can purify a changeling, cleansing them of all Banality without the unfortunate side effect of causing Bedlam. In some ways it is the most powerful and dangerous of the four stones, inevitably corrupting all but the strongest of personalities through inuring them to Banality's harshness. It sends dark dreams as well.
The Shadowstone can absorb as many points of Banality as the user has current Glamour, in effect adding to the Glamour of the user while reducing their Banality according. It also confers Stealth 5 and Subterfuge 5 on the holder. The Storyteller may require the user to make periodic Willpower rolls (difficulty 7) to avoid slipping into their Unseelie Legacy if this power is used excessively or in a spurious way. The user may also spend a point of Glamour to send troubling dreams to someone they know and can invoke "waking nightmares," extremely strong and realistic hallucinations, in others by spending two points of Glamour and accepting a point of temporary Banality themself. Such nightmares can be used to torture others.
A botch on any roll when attempting to use the stone results in the user experiencing a Nightmare at some appropriate time in the story.