Martian Madness

Martian Madness is a Hardmode, post-Plantera invasion-style event that includes several alien-themed enemies. It can be triggered after Golem has been defeated. The event includes an extremely difficult boss, the Martian Saucer.

Martian Madness is triggered when a Martian Probe spawns randomly and detects a player (turning from blue to red), and is then allowed to escape. The event can be prevented by avoiding the Probe, or by destroying it before it can escape; although destroying it is difficult, as it flies off quickly once the detection occurs or the Probe is damaged. Once triggered, the status message "Martians are invading!" appears, and UFOs start flying in the background; though Martian Madness enemies will not actually begin spawning until the player is located at their spawn point.

Escape

 * It's possible to override it with the Pumpkin Moon, Frost Moon, or other event.