Mechanical bosses

Mechanical Boss is a term which refers to any of the three Hardmode bosses that can be summoned by "Mechanical" items. Once Hardmode begins, they will begin to spawn randomly until each individual one is defeated at least once. You must slay at least one of these in order to have the Steampunker arrive. 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.