The 神秘碑牌 spawns at the entrance to the 地牢 after 石巨人 is defeated. Players cannot interact with it in any way, as it serves only as a graphical prop for the 邪教徒s' ritual and the spawning of the 拜月教邪教徒 Boss.
The Mysterious Tablet spawns surrounded by four initially-passive Cultists, two of them being 拜月教忠教徒s and the others being 蓝邪教徒弓箭手s. When all four Cultists are killed, the Lunatic Cultist spawns, destroying the Tablet, and starting the boss fight. However, nothing will happen if you do not kill all of them.
The Mysterious Tablet will respawn (including the Cultists) after one in-game day, if the player runs away or 死亡 during the Lunatic Cultist fight, when all 4 天界塔 are destroyed, or when the world is closed and restarted. Restarting the world can be the fastest option to reset them to their original state.