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, and seems to draw power from it.

Trivia

 * It seems to have a miniature Moon Lord on it.
 * It may also be portraying Cthulhu, as its in-game appearance has a glowing brain and eyes, referencing the Eye of Cthulhu and Brain of Cthulhu.