- For strategies on how to defeat the Skeletron, see Guide:Skeletron strategies.
- Not to be confused with Skeleton, an enemy found underground.
- For the stronger variation in Hardmode, see Skeletron Prime.
Skeletron is a Boss enemy that guards a world's Dungeon. To summon this boss, you must talk to the Old Man at the entrance at night, who will transform into Skeletron. If you attempt during the day, he will ask you to return during the night. If you enter the Dungeon before killing him, Dungeon Guardians will attack at 0 depth, dealing 1000 damage, effectively killing the player in one hit.
Skeletron is a massive floating skeleton head with floating arms. It will try to make contact with the player with his head and hands. His head has 4,400 health points and 10 defense, and is the most resilient entity in the game prior to the Wall of Flesh and Hardmode bosses. Destroying the head kills Skeletron. If the player takes too long to kill him and it turns to day, Skeletron will act like a Dungeon Guardian and kill the remaining players on the screen (note: it is still possible to kill him, but players are at an extreme disadvantage).
Skeletron alternates between two attacks. In the first one, his head will remain above and he will slash you with his arms. In the second one, he spins his head to attack you, dealing significant damage. However, during this second attack, his defense drops to 0.
Once you defeat Skeletron, you may enter the dungeon as many times as you like and the Clothier will move into a vacant House. You may also re-enact the fight against Skeletron by equipping the Clothier Voodoo Doll and killing the Clothier.
- The Old Man who stands in front of the dungeon can be killed if you manage to deplete his health. However, this does not count as a Skeletron kill, causing him to be able to respawn. Entering the dungeon will still allow Dungeon Guardians to spawn.
- If you use a Magic Mirror, Skeletron won't follow you back to your spawn.
- Skeletron disappears when all nearby players are dead, and the Old Man will respawn shortly after. 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.
- He is not immune to the Frostburn debuff.
- Skeletron was the first boss to drop a mask, which was added in 1.2.
- Although there is no relation, The LEGO Movie happens to have a robot skeleton named Skeletron, much like the boss's hardmode counterpart.
- 126.96.36.199: Skeletron now spawns on the Clothier when using a Clothier Voodoo Doll.
- Can now be re-summoned with the Clothier Voodoo Doll.
- Has additional item drops. (Previously only dropped Lesser Healing Potions and money.)
- Head health decreased to 4400 and damage increased from 30 to 32.
- Hands health decreased to 600, defense decreased from 18 to 14 and damage decreased to 20.
- Head health decreased from 6000 to 5000, defense decreased from 12 to 10 and damage decreased from 35 to 30.
- Hands health decreased from 1200 to 800 and damage decreased from 30 to 25.
- Pre-Release: Introduced.