To trigger the Celestial Event, the player must defeat a group of Ancient Cultists outside the world's dungeon. This attracts the wrath of the Lunatic Cultist, who utilizes magic spells to create decoys, summons Phantasm Dragons, and more, to attack the player. If the player is killed by the cultist, the group of cultists will spawn back outside the dungeon the next day, so that another attempt can be made.
After defeating the Lunatic Cultist, the main portion of the event starts, heralded by the message, "Celestial creatures are invading!" Four pillars spawn across the world, with each having their own enemies, music, and backdrops. Each pillar has 20,000 , and spawn with an invincibility shield that can only be taken down by defeating the enemies that defend them. You can tell if the pillars are vulnerable without seeing them if the enemies stop giving off particle effects when killed that move towards the pillar. Many times, the player will be overwhelmed by them spawning everywhere, as they are dangerous as well. Neither the pillars nor the enemies drop coins.
- Main article: Moon Lord
Once the four pillars are destroyed, a message reads, "Impending doom approaches...", and the screen starts to blur and shake. This signals the arrival of the Moon Lord, who takes roughly a minute to spawn after the last pillar's destruction. The Moon Lord is considered the final boss of Terraria, and is one of the most difficult fights a player will encounter. Losing to the Moon Lord will cause him to disappear, and the cultists will respawn.
- Added to the game.