Skeletron

Info
Skeletron is one of the hardest Pre-Hardmode bosses, second only to the Wall Of Flesh. It takes the form of a large floating skull, and two non-damaging arms with deadly skeleton hands on the end of them. Skeletron has no legs or body of any sort. His Mechanical counterpart is Skeletron Prime, who has four arms instead of two. The game says that Skeletron is the lingering soul of a dead prisoner in The Dungeon. Skeletron shares a resemblance to the Dungeon Guardians, who may also be souls of the deceased. Skeletron has trapped an Old Man at the dungeon, and the only way to free him is to defeat Skeletron. I

Skeletron will attack the player with his hands, using many different moves to hurt the player with them, the main one being swinging them at the player violently, and from a distance. After attacking the player with his hands for twenty seconds, he will disregard them altogether and begin to spin his head, while moving it toward the player at a fast pace. In Expert and Master Modes, you can get trapped in the middle of Skeletron's head while he spins it, dealing enough damage to kill you and end the Bossfight. Also, on Expert and Master Modes, Skeletron will shoot Homing Skulls from his head when one hand is defeated. These Homing Skulls will get faster and more frequent when the second hand is defeated, and as the head takes damage.

To summon Skeletron, you must talk to the Old Man at the dungeon, who will be there all day and all night unless you have previously defeated, or failed to defeat Skeletron. Talking to him at night will reveal the Curse option, which when pressed will summon Skeletron, and despawn the Old Man. If you fail to kill Skeletron, the Old Man will respawn later the following in-game day. If you have already killed Skeletron, you can use the Clothier Voodoo doll, which is a rare drop from enemies in The Dungeon. To use it, you must equip it in your inventory, and then kill the Clothier NPC at night. This will spawn Skeletron, but it will not consume the Clothier Voodoo Doll.

Strategies

 * If possible, always have a nearby house with a nurse and a dryad living there. The nurse can completely refill your health for a few silver coins, and the Dryad generates the 'Dryad's Blessing' debuff which increases your defence. She also generates the Dryad's Bane debuff that negatively effects enemies. Also, make a long, flat arena, with heart lanterns, Campfires and Fireflies/Stars In Bottles.
 * Use the Slimy Saddle dropped by King Slime upon death, this will allow you to jump on Skeletron's head as it spins. Even better, he raises his hands above his head as you do this, but he does not attack with them, allowing you to freely attack them for the period Skeletron's Head spins.
 * In Expert and Master Modes, Skeletron's head has 50 defense when both arms are alive. This means any obtainable weapon you can find Pre-Hardmode will only do 1 damage to Skeletron's head. This means you will have to kill both arms before you attack the head. Killing the arms should be done with a melee weapon. If you are in Expert or Master Modes, the Fiery Greatsword is recommended as the best Pre-Skeletron sword obtainable. When both arms are killed, a fast-shooting ranged weapon is recommended, such as the Minishark.
 * You may get trapped inside of Skeletron's Castle, so therefore it is recommended that you completely destroy it, and instead cover your arena in wooden platforms to give you helpful advantages. Also, the hole down to Skeletron's Dungeon should be covered with Dirt or by other means, to prevent falling in while fighting Skeletron and being murdered by the Dungeon Guardians

Achievements and Usefulness
For defeating Skeletron, you earn the Boned Achievement




 * Defeating Skeletron grants access to the Dungeon, where you can find many, many helpful things. The most helpful of them all is the Murmasa, a sword and ingredient in The Night's Edge.
 * By defeating Skeletron, you free the Old Man of hid curse, and he then becomes the Clothier.
 * Killing Skeletron is the first step to unlocking the Lunatic Cultist.