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.

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Pixie - Official Terraria Wiki

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Terraria 1.4.4 - Mechdusa How To Summon New Boss

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