Mechdusa - Official Terraria Wiki

Mechdusa is an early Hardmode boss exclusive to Get fixed boi worlds. Technically, it is not considered a separate boss, but is merely a combination of all three mechanical bosses. It resembles a large serpentine-like creature composed of the three bosses: The Destroyer's head is attached to the Skeletron Prime's head, and The Twins are individually connected via tendrils to Skeletron Prime's eye sockets instead of to each other. There are also two extra Probes attached to The Destroyer's head.

Bosses - Official Terraria Wiki

Terraria: Defeating the New Secret Boss Mechdusa (secret seed

Moon Lord - Official Terraria Wiki

Steam Workshop::Summon Mechdusa

I just deafeated moon lord and empress of light and its says that

mechdusa : r/Terraria

Skeletron Prime, Total Terraria Universes Wiki

According to the official Terraria lore, Skeletron is Cthulhu's

Wall of Flesh - Official Terraria Wiki

Medusa - Official Terraria Wiki

Category:Boss NPCs - Terraria Wiki

Just found out about legendary mode, I guess I'll try : r/Terraria