Mysterious Tablet

The Mysterious Tablet spawns at the entrance to the Dungeon after Golem is defeated. Players cannot interact with it in any way, as it serves only as a graphical prop for the Cultists' ritual and the spawning of the Lunatic Cultist boss.

The Mysterious Tablet spawns surrounded by four initially-passive Cultists, two of them being Lunatic Devotes and the others being Blue Cultist Archers. 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. It will reappear in front of the Dungeon again along with the Cultists after certain requirements are met.

Requirements

 * 1) The player dies from the Lunatic Cultist or one of the Celestial Pillars or even the Moon Lord itself.
 * 2) The player goes far away from the Lunatic Cultist, causing it to despawn.

Trivia

 * It appears to have the face of the Moon Lord on it.
 * The Chlorophyte armor's Leaf Crystal may fire at the Tablet, which may lead to the player accidentally making the Cultists aggressive.
 * The tablet, along with the Cultists that surround it, will re-spawn after one in-game day, or if the player defeats Golem or the Moon Lord.

History
Tablette Mystérieuse