The Cintamani Stone is a mythical object within the city of Shambhala, featured in Among Thieves. It also appears as a Mystical in the multiplayer for A Thief's End. As a Mystical, if thrown it restores the health of any downed teammate to 40% within its radius.
In real life the Cintamani Stone is said to be a wish-fulfilling jewel, within both Hindu and Buddhist traditions.
The first reference to the Stone in Among Thieves came from a hidden text on a page by Marco Polo. In "Breaking and Entering", after acquiring the Mongolian oil lamp, Nathan Drake and Harry Flynn managed to reveal the invisible ink which talked about "the curse of the Cintamani". They presumed that Polo was in possession of the Stone, and that it would still be on the site of the lost fleet in Borneo.
Later, after Flynn's betrayal, Nate talked to Chloe Frazer and Victor Sullivan, explaining to the latter that Polo called it a deep-blue sapphire, with proportions wider than that of a man's arms. Chloe also added that Zoran Lazarević had been after the Stone for years. In "The Dig", Nate learned that Polo never actually took the Stone from Shambhala, and that Lazarević was looking for something else in Borneo.
In "They're Coming With Us" he also talked about the Stone with Elena Fisher after he spotted a symbol of it on the temple they were looking for. Much later again, in "Where Am I?" he learned that the Nazis had sent an expedition, led by Karl Schäfer, to try and find Shambhala and steal the Stone. Schäfer clarified that the Stone's power was true, and that some past rulers like Genghis Khan and Tamerlane managed to succeed due to being in possession of a sliver of the Stone.
Per Schäfer's direction Nate went to the ice temple, where he saw several depictions of the Stone being held by monstrous figures. Nate realized what Schäfer was talking about and decided to try and stop Lazarević, even at great risk to himself. He, Elena, and Chloe, ultimately succeeded in reaching the Stone in time, at which point Nate realized Polo had been entirely wrong. The Cintamani stone was not a sapphire, but amber; a giant orb of fossilized resin. The Stone can be considered either lost or destroyed alongside the destruction of the city at the end of events in "Tree of Life".
- Beer, Robert (2003). The Handbook of Tibetan Buddhist Symbols. Serindia Publications, Inc. ISBN 9781590301005.