Mysterious Tablet

The Mysterious Tablet spawns at the entrance to the Dungeon and is surrounded by the four initially-passive Cultists. When all four cultists are killed the Lunatic Cultist spawns, causing the Tablet to break and disappear when the Cultist breaks it. It seems it has some type of otherworldly power in it, which may be released by the Lunatic Cultist when he is defeated, which would mean the energy from the Tablet triggered the Lunar Events.

Trivia

 * It appears to have the face of the Moon Lord on it.
 * The Chlorophyte armor will shoot a Leaf Crystal at the tablet, which may lead to the player accidentally making the cultists aggressive.