The Sorcerer's Tombstone

Missing, extremely new, or very obvious to obtain.

In the Chinese version (灵鹫宫石壁; lit. Stone wall in Lingjiu Palace), it is a reference to the wuxia novel "Demi-Gods and Semi-Devils" by Jin Yong. In the novel, Lingjiu Palace is the base of Tianshan School, established by Tianshan Tonglao. On top of the mountain, there's a chamber where the martial arts of her school were inscribed on the stone wall, but they all are of extremely high level that most people can't decipher. Anyone who insisted on reading without sufficient strength and knowledge would go mad or even die. - Credit: Necrosyrtes