Mechanical bosses

Main article: Boss

The Mechanical Bosses are three Hardmode Bosses that can be summoned by "Mechanical" items, and are themselves metallic and robotic in appearance. In addition, there is a 10% chance that one will randomly spawn each night 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 Hardmode Anvil. Each also drop from all Hardmode enemies (except statue-spawned enemies and Meteor Heads) with a 1/2500 chance until their respective boss is defeated.

Once any single Mechanical Boss has been defeated for the first time:

• The Steampunker will arrive (if a vacant house is available).
• The Truffle will begin selling the Mushroom Spear and Hammush.
• Solar Eclipses start to occur.
• 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,  Windows Phone, and 3DS 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
• Old One's Army upgrades to Tier 2 and will progress to wave 7 (however, Betsy will not spawn until Golem is defeated).
• Plantera's Bulbs begin spawning in the Underground Jungle.

After all three Mechanical Bosses are defeated:

• The status message "The jungle grows restless..."
• Plantera's Bulbs begin spawning in the Underground Jungle. The breaking of these is required to summon Plantera, which is required to have the ability to enter the Jungle Temple.
• Reapers and Mothrons now spawn during Solar Eclipses (on , Reapers will spawn after just one Mechanical Boss is defeated).

Boss		Spawn Message	Summoning Item		Soul Type
	The Destroyer	"You feel vibrations from deep below..." or "You feel a quaking from deep underground..."		Mechanical Worm	Soul of Might
	The Twins	"This is going to be a terrible night..."		Mechanical Eye	Soul of Sight
	Skeletron Prime	"You feel the air getting colder around you..." or "The air is getting colder around you..."		Mechanical Skull	Soul of Fright

Summoning Items Recipes

The Destroyer

Result	Ingredients	Crafting station
Mechanical Worm	Rotten Chunk6 Any Iron Bar5 Soul of Night6	Mythril Anvil or Orichalcum Anvil
	Vertebra6 Any Iron Bar5 Soul of Night6

The Twins

Result	Ingredients	Crafting station
Mechanical Eye	Lens3 Any Iron Bar5 Soul of Light6	Mythril Anvil or Orichalcum Anvil

Skeletron Prime

Result	Ingredients	Crafting station
Mechanical Skull	Bone30 Any Iron Bar5 Soul of Light3 Soul of Night3	Mythril Anvil or Orichalcum Anvil

Notes

• Bringing the Mechanical Bosses’ summoning items to a Pre-Hardmode world makes it possible to defeat them prior to defeating the Wall of Flesh. However, the Wall of Flesh must still be defeated in order to unlock Plantera.

Tips

• Players who aren't confident in their ability to defeat the bosses, but who want access to the Hardmode Ores, can refrain from destroying any Altars until they are ready and instead fish for Crates, which offer those ores and their bars as random rewards during Hardmode. Crates acquired pre-Hardmode can also be saved until Hardmode, and will still offer Hardmode rewards.
• Once one of the spawning messages appears at random, fleeing underground, or logging out and back in again, can prevent the Mechanical Bosses from spawning.
• On the  Mobile version and Nintendo 3DS version, the player can find a Drax in an Underworld Shadow Chest, allowing the player to get Turtle armor before defeating any of the Mechanical Bosses, making it much easier to defeat them on the first try.
• On the  Mobile version, Nintendo 3DS version and  Old-gen console version, if you’ve successfully defeated a mechanical boss you may want to make the Excalibur and then live through a Solar Eclipse. If you’ve obtained a Broken Hero Sword craft a True Excalibur at a Mythril/Orichalium anvil. If you have the Night's Edge and you have another Broken Hero Sword from the Solar Eclipse craft a True Night's Edge and use that instead. If you have another Broken Hero Sword use the True Night's Edge and the True Excalibur with another Broken Hero Sword you can craft the Terra Blade.

Trivia

• Some teasers for the  Mobile version release included The Destroyer having blue-lit segments instead of red.
• All of the Mechanical Bosses seem to shoot a red Death laser when in at least one of their forms.

Achievements

Buckets of Bolts • “Defeat the three nocturnal mechanical menaces: the Twins, the Destroyer, and Skeletron Prime.”

Defeat all three Mechanical Bosses.

Category: Slayer

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.

Category: Challenger

Back for Second • “You have defeated all the prime bosses twice!”

Defeat all of the Mechanical bosses twice.

History

See the individual Mechanical Bosses' articles for more specific changes.

 PC version

• 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 you have beaten all three Mechanical Bosses.

• Desktop 1.2.3.1: No longer spawn randomly if another boss is alive. You can still summon multiple bosses manually.

• Desktop 1.2.3: Now slightly more difficult.

• 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 1.1: Introduced.

 Console version

• Console-Release: Introduced.

 Mobile version

• Mobile-Release: Introduced.

Nintendo 3DS version

• 3DS-Release: Introduced.