Mechanical 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:
- The Steampunker will arrive (if a vacant house is available).
- The Truffle will begin selling the Mushroom Spear and Hammush.
- Solar Eclipses will now occur naturally.
- Red Devils and Lava Bats spawn in the Underworld.
- Enemies in the Jungle, Underground Jungle, and Jungle Temple gain a 1/200 (0.5%) chance of dropping the Yelets(Desktop, Console and Mobile versions) yoyo.
- Life Fruit will begin to grow in the Underground Jungle.
- The Traveling Merchant will begin to sell the Code 2(Desktop, Console and Mobile versions).
- The Dye Trader begins rewarding the player with Chlorophyte Dye, Living Ocean Dye, Living Flame Dye, and Living Rainbow Dye in exchange for Strange Plants.
- Old One's Army(Desktop, Console and Mobile versions) upgrades to Tier 2 and will progress to wave 7 (however, Betsy or Etherian Lightning Bugs will not spawn until Golem is defeated).
- Moss Hornets and Moths gain a chance to drop the Tattered Bee Wing and Butterfly Dust respectively.
Defeating all three mechanical bosses causes the following to happen:
- The status message "The jungle grows restless..." appears, indicating that (Desktop, Console, Old-gen console and Mobile versions) Plantera's Bulbs have begun growing in the Underground Jungle. Breaking one of these bulbs summons Plantera.
- One Plantera's Bulb immediately spawns once all three mechanical bosses are defeated for the first time.
- Reapers now spawn during the Solar Eclipse.
- The Traveling Merchant will begin to sell the Pulse Bow.
Boss | Spawn message | Summoning item | Dropped soul type | ||
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The Twins | "This is going to be a terrible night..." | ![]() |
Mechanical Eye | ![]() |
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The Destroyer | "You feel vibrations from deep below..." | ![]() |
Mechanical Worm | ![]() |
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Skeletron Prime | "The air is getting colder around you..." |
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Mechanical Skull | ![]() |
Crafting
Summoning items recipes
Result | Ingredients | Crafting station |
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Notes
- 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.
Achievements






Tips
- In order to acquire the Hardmode ores, it is not required to destroy Altars and thus expose oneself to the risk of having a mechanical boss spawn unexpectedly. Instead, it is possible to open crates, which contain Hardmode ores and bars. As of 1.4.0.1(Desktop, Console and Mobile versions), crates acquired in pre-Hardmode will not give Hardmode rewards.
- As long as the respective mechanical boss has not been defeated, its summoning item can be farmed in events with a high number of enemies, such as the Pirate Invasion or Goblin Army.
Trivia
- 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.
– 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.
History
- Desktop 1.4.4: The Pulse Bow is now sold after defeating all mechanical bosses.
- Desktop 1.3.0.1:
- Life Fruit now only spawns after defeating a mechanical boss.
- Now drop Mechanical Cart pieces in Expert Mode.
- Desktop 1.2.4: Fixed bug where "The jungle grows restless..." message would appear before all three mechanical bosses have been beaten.
- Desktop 1.2.3.1: No longer spawn naturally if another boss is alive. Multiple bosses can still be summoned manually.
- Desktop 1.2.3:
- Now slightly more difficult.
- Plantera's Bulbs now only spawn after defeating all mechanical bosses.
- The Mushroom Spear and Hammush are now only sold after defeating any mechanical boss.
- Desktop 1.2.1.1: Will no longer spawn during Pumpkin Moons.
- Desktop 1.2.1: Reduced the chance for a mechanical boss summoning item to drop during Hardmode.
- Desktop 1.2.0.3:
- 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.
- Desktop 1.1: Introduced.
- Console-Release: Introduced.
- Mobile 1.1.5822: Enabled & unlocked all Hardmode content.
- Mobile 1.1.8: Added all Hardmode content, but they are unobtainable.
- 3DS-Release: Introduced.