Skeletron is a boss which only can be summoned by talking to the Old Man in front of a dungeon at night. If you choose the "Curse" option when talking to him, he will immediately transform into Skeletron and begin attacking you, so be prepared when this happens.
If you wish to fight him again after he has been defeated, you may summon him using the Clothier Voodoo Doll. You should kill the Clothier at night after 7:30 PM and you must equip the Clothier Voodoo Doll as an accessory. Skeletron only spawns during the night. If he's not defeated before daylight, he will behave like a Dungeon Guardian, but still drop loot if defeated this way.
This is a difficult boss, do not try to fight him unless you have lots of potions, good pre-Hardmode gear and/or throwing weapons.
Going too deep into the dungeon before defeating Skeletron will cause one or more Dungeon Guardians to surface and attack the player. These Dungeon Guardians resemble Skeletron's head, have 9999 defense as well as 9999 health, and can kill a player in one hit due to dealing 1000 damage.
When you defeat Skeletron, you will gain access to the dungeon, and the Clothier NPC will come to your town if you have a house for him. As of the 1.2 patch, Skeletron also drops the Skeletron Trophy.
If you fail to kill Skeletron, the Old Man NPC will respawn at the dungeon later the following day.
Skeletron will attempt to hit you with his arms by swinging them at you and will spin his head every 20 seconds or so, put his arms in the air, and chase you with his head, very much like the Dungeon Guardian. He also often slams his arms together, attempting to crush you. If you take too long to kill him, and the sun comes up the next day, Skeletron will hit you for 9999 damage, killing you instantly, just like the Dungeon Guardian. If not on expert, you could simply focus on his head and Skeletron will be defeated if his head runs out of health before his hands do.
In Expert Mode, Skeletron's head possesses a very high resistance to damage (100 defense means it takes 50 less damage from all sources), to the point that any current accessible weapons will be rendered almost completely useless against the boss. To weaken his defense, players must destroy both of his hands--Each of which holds half of the skull's heightened defense. If a hand is destroyed, Skeletron begins to fire skulls at the player. This intensifies if his other hand is defeated, and will also increase in frequency as the health of his head drops. Skeletron's hands inflict the Slow Debuff and the Head inflicts Bleeding. His AI is improved, allowing him to deal with multiple players with more efficiency.
There are a few things to keep in mind while fighting this boss with any kind of technique.
- First, try to keep the fight on a nice flat surface. It makes Skeletron's attacks far easier to dodge and makes attacking him just as easy. Secondly, watch out for his hands, as they will usually hit you the most often. Lastly, always watch for when he is rolling his head. While attacking like this he is extremely vulnerable because of reduced defense, and more damage can be done against him. Also, start the fight at the earliest possible time because he needs to be defeated before daylight.
- Probably the most common method is to use Ranged Weapons. Simply spamming your shots at Skeletron's head while dodging his attacks is usually quite effective, especially if your weapon has rapid fire. Good weapons to use would be the Sandgun (if you don't mind sand getting covered all over the surrounding area), Minishark or Star Cannon (assuming you can afford the strange form of ammunition). The Molten Fury with Hellfire Arrows are also a good choice. Shuriken and Throwing Knives are a possible but challenging way to kill Skeletron earlier in the game. Space Gun with full set of Meteor Armor is practically the most powerful because not only you can use the weapon limitlessly, it also has a reasonable amount of base damage.
- Another technique to better conserve ammo is to use ranged weapons to attack Skeletron's hands first, and then deal with the head using swords that can hit behind you, flail weapons or weapons that return to you, like the Flamarang.
- Yoyos like Amazon and Code 1 are good weapons to use with while Skeletron's head is spinning. It can deal very high damage (around 60/s if you aim it correctly), especially if you reforge it to a better one like Godly and Ruthless. Yoyos can be the perfect type of weapon because of the long range, high damage and you will be safe if you keep a distance between you and the spinning head that deals very high damage.
- Another easy technique is to throw Spiky Balls along the floor, which will destroy Skeletron's arms fairly quickly. After its arms are destroyed, proceed as normal to destroy the head when doing so use your remaining spiky balls to make him spin his head in it dealing serious damage. This is also a useful technique for fighting the Eater of Worlds, as each segment will take damage upon passing through a Spiky Ball.
- For more safety, try to wear Molten Armor (you might need to defeat the Eater of Worlds first for the Hellstone mining unless you have Reaver Shark from fishing) for the highest armor set defense in pre-hardmode, and build a house near the dungeon and let the Nurse NPC to settle there for emergencies like low on health so you can get instant healing to max health. For even more safety, build a very big arena with box-shaped using platforms (12 boxes, 4x3, each box is around 20x35). Then when he is close to you, grapple yourself to a wall for quick escaping using Grappling Hooks. Molten Armor allows you to take much less damage.
- If you are playing on Mobile, PC or console versions, having a dryad nearby would give you the 'Dryad's Blessing', which increases your defence.
- Equipping the slime mount dropped by King Slime allows you to jump on Skeletron's head when it is spinning and not suffer any damage. While doing this, he raises his hands above his head but does not attack with them, allowing you to hit them freely for the period his head spins.
- A graphical bug appears when you fail to kill Skeletron before dawn but survive (if he flies too far off screen) and see the Old Man spawn, when you kill Skeletron, multiple Skeletron heads will appear and there will be more loot as a consequence.
- If Skeletron spawns too far outside the dungeon, his hands despawn.
- Rarely when you spawn Skeletron, The Twins may spawn even if you're not on Hard Mode yet.
- As of PC 1.1, Skeletron has a tougher, more intimidating mechanical variant known as Skeletron Prime. It has 4 arms, has a metallic look and its head is covered in spikes during it's head-spin attack. He also behaves like the Dungeon Guardian in daylight.
- He will no longer revert to regular form once it's daytime. Although if the player manages to defeat him, the relevant achievement will be obtained, loot drops as normal and access to Dungeon is granted (Dungeon Guardians also no longer appear).
- Prior to 1.2, Skeletron was the only boss that could only be summoned and defeated only once per world.
- Killing Skeletron now earns the achievement "Boned"
- Now has a larger number of possible drops.
- Can now be summoned using a Clothier Voodoo Doll.
- Head's health decreased from 5,000 HP to 4,400 HP.
- Head's health decreased from 6,000 HP to 5,000 HP and defense decreased from 12 to 10.
- Added to the game.
Skeletron Prime - Mechanical variant, much more powerful.