Mysterious Tablet

The Mysterious Tablet is a background object which 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 Devotees and the others being Blue Cultist Archers. Once all four Cultists are killed, the Lunatic Cultist spawns, destroying the Tablet, and starting the boss fight.

The Mysterious Tablet will respawn (including the Cultists) after one in-game day, if the player runs away or dies during the Lunatic Cultist fight, when all four Celestial Pillars are destroyed, or when the world is closed and restarted. Restarting the world can be the fastest option to reset the Tablet and the Cultists to their original state.

Trivia

 * The Mysterious Tablet resembles the Celestial Sigil, a boss-summoning item used to summon the Moon Lord. It appears to have the Moon Lord's face on it.
 * The Mysterious Tablet, along with the Cultists, can have its spawn slightly changed by moving the blocks directly above and below them.
 * Bees are the only enemy in Terraria that can damage the Mysterious Tablet. They can be spawned e.g. by mining Hive blocks or summoning Queen Bee, and will damage and eventually destroy the Tablet if they come into contact with it. As of, Bees are unable to damage the Mysterious Tablet.
 * The Lunatic Cultist cannot spawn if the Tablet is not alive. Therefore, destroying the Tablet with Bees first and then killing the Cultists will not spawn the Lunatic Cultist.
 * This is an easy way to fill the Bestiary entries for Lunatic Devotees and Blue Cultist Archers.
 * It is worth noting that Bees can kill the Lunatic Devotees and Blue Cultist Archers.
 * If the Tablet is spawned in and made vulnerable using third-party software, or attacked by Bees, it can be heard that the hurt sound is the same as the mechanical bosses', and the death sound is an explosion.

History
Mysteriöse Tafel Tablette mystérieuse 神秘碑牌