Mechanical bosses

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Main article: Bosses

The term "mechanical bosses" refers to three early-Hardmode bosses; The Twins, The Destroyer, and Skeletron Prime, which are grouped together under this generic term due to sharing certain characteristics: They can be summoned by "mechanical" items, and are themselves metallic and robotic in appearance, resembling mechanized versions of pre-Hardmode bosses, namely the Eye of Cthulhu, Eater of Worlds, and Skeletron, respectively. In addition, there is a 1/10 (10%) chance that one will randomly spawn each dusk after the first Demon/Crimson Altar is destroyed in a world, and each will continue to spawn randomly until it is defeated at least once.

The mechanical bosses' summoning items can be crafted at a Mythril or Orichalcum Anvil. They also drop from all Hardmode enemies (except statue-spawned enemies, Meteor Heads, and Old One's Army enemies) with a 1/2500 (0.04%) chance until their respective boss is defeated.

Defeating any single mechanical boss for the first time will cause the following to happen:

Defeating all three mechanical bosses causes the following to happen:

Boss Spawn message Summoning item Dropped soul type
The Twins The Twins "This is going to be a terrible night..." Mechanical Eye Mechanical Eye Soul of SightSoul of Sight
The Destroyer The Destroyer "You feel vibrations from deep below..." Mechanical Worm Mechanical Worm Soul of MightSoul of Might
Skeletron Prime Skeletron Prime "The air is getting colder around you..." Mechanical Skull Mechanical Skull Soul of FrightSoul of Fright


Summoning items recipes

ResultIngredientsCrafting station
Mechanical EyeMechanical EyeMythril AnvilMythril Anvil
Orichalcum AnvilOrichalcum Anvil
Mechanical SkullMechanical Skull
Mechanical WormMechanical Worm


  • When spawning naturally, a mechanical boss spawns exactly 81 in-game minutes (at 8:51 PM) after the status message has appeared. Being in a layer lower than the Surface at that moment, or, in singleplayer, exiting the world during that timespan, will prevent the boss from spawning naturally.
  • With the 1/10 (10%) chance of spawning naturally at dusk, the resulting chance for each mechanical boss is initially 1/30 (3.33%). Once one of them has been defeated, the remaining two have a resulting 1/20 (5%) chance of spawning naturally, and after defeating the second one, the last one has the full chance of 1/10 (10%).
  • An Eye of Cthulhu naturally spawning will take precedence over a mechanical boss naturally spawning.[1]
  • A Lantern Night(Desktop, Console and Mobile versions) occurring will prevent a mechanical boss from naturally spawning. However, summoning a mechanical boss using one of the summon items will cancel out the Lantern Night, just like any other boss summon.
  • In a Get fixed boi(Desktop, Console and Mobile versions) world, the player cannot summon the mechanical bosses separately, they have to summon the Mechdusa instead.
  • It is possible to summon a mechanical boss in pre-Hardmode if the summoning item is brought in from another world. However, if the Wall of Flesh has not been defeated, Plantera's Bulbs will not start spawning.


Achievement Buckets of Bolts.png
Buckets of Bolts • Defeat the three nocturnal mechanical menaces: the Twins, the Destroyer, and Skeletron Prime.
Defeat all three mechanical bosses. (Desktop, Console and Mobile versions)
Category: Slayer Slayer
Achievement Mecha Mayhem.png
Mecha Mayhem • Do battle against the Twins, the Destroyer, and Skeletron Prime simultaneously and emerge victorious.
Defeat all three mechanical bosses simultaneously in a single battle. (Desktop, Console and Mobile versions)
Category: Challenger Challenger
Achievement Slayer of Worlds.png
Slayer of Worlds • Defeat every boss in Terraria.
Defeat every boss in the game. (Desktop, Console and Mobile versions)
Category: Challenger Challenger
Achievement Back for Second.png
Back for Second • “You have defeated all the prime bosses twice!”
Defeat all of the mechanical bosses twice. PlayStation 3



  • All of the mechanical bosses shoot a red Death Laser: the Destroyer's segments, Retinazer in its second phase, and the Prime Laser.
  • They are the only bosses whose Expert(Desktop, Console and Mobile versions)-exclusive items are crafting materials.
  • Terraria lore pages – According to the Terraria lore pages, the mechanical bosses are likely the parts of Cthulhu which the Mechanic was forced to build. This explains the lack of a mechanical counterpart of the Brain of Cthulhu, as the mechanical Cthulhu lacks a brain and the Mechanic was never able to finish it.


See the individual mechanical bosses' articles for more specific changes.
  • Desktop 1.2.4: Fixed bug where "The jungle grows restless..." message would appear before all three mechanical bosses have been beaten.
  • Desktop No longer spawn naturally if another boss is alive. Multiple bosses can still be summoned manually.
  • Desktop 1.2.1: Reduced the chance for a mechanical boss summoning item to drop during Hardmode.
  • Desktop
    • Hardmode Crimson, Corruption, and Hallow spread is now slowed after killing Plantera instead of any mechanical boss.
    • Slightly increased the chance for a Solar Eclipse to happen, but they will now only happen after killing a mechanical boss.
  • Desktop 1.2:
    • Now slightly less difficult.
    • Now have a 1/10 (10%) chance to spawn at dusk until defeated for the first time.


  1. Information taken from the Desktop version Desktop source code, method UpdateTime() in Terraria.Main.cs. There may be inaccuracies, as the current Desktop version Desktop version is