Celestial Event

The  is a hardmode event that begins once the player defeats the Golem, followed by the Lunatic Cultist.

Lunatic Cultist
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 Spectral 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.

Celestial Pillars
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.

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.