Skeletron alternates between two attack phases: Each part can be killed independently, but killing the head is all that is required to defeat Skeletron. All parts can travel through blocks, and will attempt to make contact with the player to inflict damage. Skeletron is a large floating skull with two independent floating hands. Killing the Clothier using Flymeal will not summon Skeletron unless the Clothier Voodoo Doll is equipped. Skeletron can be re-summoned thereafter once the player acquires the Clothier Voodoo Doll (from Angry Bones or Dark Casters), then by attacking and killing the Clothier during night. Once it is defeated, the Old Man's curse will be lifted and he will no longer appear. Skeletron can be summoned repeatedly this way until it is defeated.
While players with less than 300 maximum health and/or less than 10 defense are deemed too weak by the Old Man to lift his curse, he still offers the option to summon Skeletron. Skeletron can only be summoned once per night, as the Old Man will not respawn until dawn. If the Old Man is spoken to during the day, he will ask the player to return at night. Skeletron is summoned by speaking to the Old Man at the Dungeon's entrance at night, who will turn into Skeletron when selecting the ' Curse' option.