Skeletron

"Please, no, stranger. You'll only get yourself killed!"

Skeletron is a Boss that must be defeated before traveling through the Dungeon. It is immune to the Poisoned, On Fire!, and Cursed Inferno debuffs.

Defeating Skeletron grants unlimited access to all Dungeon areas for all players. It also causes the Clothier NPC to spawn, so long as a vacant House is available.

If you enter the Dungeon before killing Skeletron, Dungeon Guardians spawn once you reach 0 depth, generally killing any player with a single hit.

Summoning
Skeletron is summoned by speaking to the Old Man at the Dungeon's entrance, at night, who will die and spawn Skeletron when you select the “curse” option. If you speak to the Old Man during the day, he will ask you to return at night.

Skeletron can be summoned repeatedly this way until it is defeated. Once it is defeated, the Old Man will no longer appear. Skeletron can be re-summoned thereafter once the player acquires the Clothier Voodoo Doll. Equipping the Doll allows the player to kill the Clothier, which summons Skeletron.

Attacks
Skeletron is a large floating skeleton head with two independent floating hands. All parts can travel through blocks, and will attempt to make contact with the player to inflict damage. Each part can be killed independently, but killing the head is all that's required to defeat Skeletron.

Skeletron alternates between two attacks:
 * The head remains above while his hands slash at the player.


 * The head spins, dealing significant damage, but its defense drops to zero.

Skeletron has an additional attack in expert mode: If the player takes too long to kill him and dawn arrives, Skeletron will act like a Dungeon Guardian, performing a head spin attack with very high damage, which will usually kill any players remaining in the vicinity quickly (it is still possible to kill him, but players are at an extreme disadvantage).
 * After losing both his arms he will continue to shoot homing skulls at the player.

Tips

 * With multiple players, it's a good idea for softcore and mediumcore characters to set up a Bed near the Dungeon, so that they can simply rejoin the fight if they die.
 * If you use a Magic Mirror, Skeletron won't follow you back to your spawn, and despawn instead.
 * In expert mode, Skeletron has extremely high defense until you defeat the hands.

Trivia

 * Assuming that the player is at 5 ft. 9 1⁄2 in. heightwise, Skeletron's Head would be about 11 feet tall and 8 feet wide. The Hands would be 10 feet tall and 7 feet across.
 * Skeletron Heads used to protect the Dungeon, but when one was killed, it would count as killing Skeletron, so they purposed the Dungeon Guardians to protect the Dungeon instead.
 * The name Skeletron could be reference to Skeletor, one of the characters from Masters of the Universe.

History
Skeletron Скелетрон