Mechanical bosses

Mechanical Boss is a term which refers to any of the three Hardmode bosses that can be summoned by "Mechanical" items, which are listed below. Once Hardmode begins, they will begin to spawn randomly until each individual one is defeated at least once. There is a 10% chance that one will be spawned each night, the only condition being destruction of a single Demon/Crimson Altar.

Once any Mechanical Boss has been defeated for the first time:
 * The Steampunker will arrive if there is a house available
 * The Truffle will begin selling the Mushroom Spear and Hammush
 * Solar Eclipses can occur
 * Red Devils and Lava Bats will spawn in the Underworld

After all three Mechanical bosses have been slain at least once each, the message "The jungle grows restless" will appear, and Plantera's Bulb will begin to grow in the Underground Jungle.