The Celestial Sigil is a boss-summoning item crafted out of 20 of each of the Celestial Tower's fragments. It is used to summon the Moon Lord without going through the Lunar Events. The Lunar Events must not be active (there cannot be Celestial Towers in the world) to use the item. This item cannot be used when you are able to see the Lunatic Devote and/or Blue Cultist Archer on your screen, or when another boss has already been summoned. It also cannot be used in a world in which Golem has not been defeated. Note that rather than summoning the Moon Lord immediately after the item is used, it takes about a minute before the Moon Lord actually appears, the same way as when all of the pillars are defeated.
- It resembles the Mysterious Tablet, the strange idol near the Dungeon, which helps trigger the Lunar Events.
- The four colors on the rim of the sigil represent the colors of the four Celestial Towers.
- The item was implemented to reduce the amount of time required to farm the Moon Lord. Before 184.108.40.206, simply reaching the Moon Lord could take upwards of 10 to 15 minutes.
- Due to the high amount of fragments needed, the player may only have enough fragments after 1 event to craft 1 or rarely 2 of these. In expert mode it is possible to get enough to make 3.