The X are parasitic organisms discovered on SR388 that can infect any living creature. They kill their hosts and absorb their DNA to assume the host's form. An X that has possessed multiple hosts can combine their appearances and traits during the process of replication and morph into a new entity.

Quiet Robe X appears before her, and despite Samus immediately raising her guard by pointing her arm cannon at him, he greets her in a similar manner as he did in life, turns into a red X and willfully lets Samus absorb him to neutralize her powers to allow her to touch the controls without draining it, and she managed ...

While created through different means, both are shown to be powerful adversaries who tested Samus' abilities. However Dark Samus was shown to have more personality, while SA-X was simply an X Parasite mimicking Samus at her full power.

Metroid Fusion[edit] At the start of Metroid Fusion, whilst Samus is on a mission by the Galactic Federation to escort researchers upon the planet SR388, she encounters an X-infected Hornoad. She easily destroys it, though the leftover X-parasite flies into Samus.