The term "mechanical bosses" refers to three Hardmode bosses; The Destroyer, The Twins, 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 mechanical versions of the pre-Hardmode bosses Eater of Worlds, Eye of Cthulhu, and Skeletron, respectively. In addition, there is a
10*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
0.04*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.
- Yelets can be dropped by any enemy in the Jungle biome.
- Life Fruit will begin to grow in the Underground Jungle (on the Old-gen console and versions, Life Fruit begins growing in small numbers when Hardmode is initiated; more will grow after a mechanical boss is defeated).
- The Traveling Merchant will begin to sell the Code 2.
- 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 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.
- Plantera's Bulbs begin spawning in the Underground Jungle, allowing Plantera to be summoned.
Defeating all three mechanical bosses causes the following to happen:
- The status message "The jungle grows restless..." appears, indicating that Plantera's Bulbs have begun growing in the Underground Jungle. Breaking one of these bulbs summons Plantera.
- On the Desktop version, Console version, and Mobile version, 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|
|The Destroyer||"You feel vibrations from deep below..."||Mechanical Worm||Soul of Might|
|The Twins||"This is going to be a terrible night..."||Mechanical Eye||Soul of Sight|
|Skeletron Prime||"The air is getting colder around you..."||Mechanical Skull||Soul of Fright|
Summoning items recipes
|Mechanical Eye||Mythril Anvil|
- 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
10*1/10 (10%) chance of spawning naturally at dusk, the resulting chance for each mechanical boss is initially 3.33*1/30 (3.33%). Once one of them has been defeated, the remaining two have a resulting 5*1/20 (5%) chance of spawning naturally, and after defeating the second one, the last one has the full chance of 10*1/10 (10%).
- An Eye of Cthulhu naturally spawning will take precedence over a mechanical boss naturally spawning.
- A Lantern Night 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.
- It is possible to summon a mechanical boss 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.
- 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 126.96.36.199, crates acquired pre-Hardmode will not give Hardmode rewards.
- On the Nintendo version, the player can find a Drax in an Underworld Shadow Chest, allowing the player to acquire Turtle armor before defeating any of the mechanical bosses, making it much easier to defeat them on the first try.
- On the Old-gen console version and Nintendo version, it is possible to obtain a Terra Blade after defeating a single mechanical boss. Note that three Broken Hero Swords (As opposed to one) from a Solar Eclipse will be required, however.
- 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.
- 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-exclusive items are crafting materials.
- – According to the official game lore, 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.
- Desktop 1.4.4: The Pulse Bow is now sold after defeating all mechanical bosses.
- Desktop 188.8.131.52:
- 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 184.108.40.206: 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 220.127.116.11: 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 18.104.22.168:
- 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
10*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.