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Skeletron is a boss.It must be defeated before entering the dungeon, and it grants unlimited access to all areas for all players.As long as there is a vacant house, the Clothier NPC can be spawned.

If attempting to enter the dungeon before killing Skeletron, there will be a dungeon guardian.The enemies deal 1000 / 2000 / 3000 damage and kill any player with a single hit.If you want to enter the dungeon, defeating Skeletron is mandatory.

The music Boss 1 will play while Skeletron is alive.When Otherworldly music is enabled, the track Boss 1 will play instead.

The Old Man at the dungeon's entrance at night will turn into Skeletron when selecting the "Curse" option.The Old Man will ask the player to come back at night if he is spoken to during the day.The Old Man will not leave until dawn, so Skeletron can only be summoned once per night.The option to summon Skeletron is still available to players with less than 300 maximum health and 10 defense.

Skeletron can be summoned multiple times until it is defeated.The Old Man's curse will be lifted once it is defeated.The Clothier will look a lot like the Old Man.If there is an empty house for him to live in, he can move to a town.Once the player acquires the Clothier Voodoo Doll, Skeletron can be re-summoned.The Clothier summons Skeletron if the accessory is Equipping.This will only work at night.Skeletron doesn't spawn on any other occasions.