SA-X

The SA-X is a video game character from the Metroid series of games. It appeared in Metroid Fusion, in which it was a copy of the main character Samus Aran. The SA-X was originally an X Parasite that copied Samus Aran's abilities on one of her trips to the planet SR388 and dwelled within her until it was surgically and biologically removed. The SA-X's name means that is an X copy of Samus. The letters S, A, and X stand for Samus Aran and X (as in "X Parasite" or representing an unknown or different version), respectively.

Metroid suit
The infected Power Suit was transported to a B.S.L. Research Station in orbit above SR388. But it escaped its containment cell using one of Samus' Power Bombs and set free all the X Parasites in the Quarantine Bay. Samus was sent to the station to find all crew members dead and the X infesting several sections of the station. Her initial investigations accidentally allowed the X access to some of the breeding environments by releasing security locks. Subsequently, the SA-X manipulated Samus by destroying doors and wreaking havoc in certain areas to release all the security locks and allow the X Parasites access to all breeding areas. Though ADAM warns Samus of ten SA-X aboard the station, only two are seen - one is destroyed when the Restricted Area self destructs; the second (which is implied to be the same one encountered everywhere else) confronts Samus after she set the station on a course to hit the planet SR388, and later returns to try to defeat the Omega Metroid. The Omega Metroid defeats this SA-X which subsequently provides Samus with her coveted Ice Beam to defeat the Omega Metroid, in a similar fashion to the Hyper Beam from the ending of Super Metroid, which was used to defeat Mother Brain.

During the course of the game, Samus discovers a secret laboratory on the station that is cultivating Metroids, which the SA-X promptly ravages (and is subsequently devoured by several Metroids). After the lab is detached from the station with the SA-X on board, Adam, Samus' computerized CO, explains that the SA-X has been reproducing and that now there are no fewer than ten SA-X onboard.

The SA-X is extremely dangerous in close combat, mimicking Samus at the height of her powers. It is equipped with the Screw Attack and Space Jump, and fires beam shots appearing to be a combination of the Plasma, Ice, and Wave beams. It cannot be damaged by Samus until the final fight against the SA-X.

Samus prevails over another SA-X in close combat, which morphed into a large monster after several Charge Beam shots. After the SA-X physical form, monster, and Core-X are destroyed, the parasitic SA-X escapes before she can absorb it (as she did other X Parasites). This SA-X resurfaces a short time later, after Samus had set the B.S.L. station on a collision course, during Samus' final battle with the Omega Metroid, when Samus is about to be killed. The SA-X fends off the Omega Metroid but is then fatally wounded, returning it to its parasitic state (some suggest that the SA-X came back and fought the Omega Metroid because the X were hunted by Metroids. Another theory is that knowing Samus had set the station to explode on SR388, the X determined that only way for them to survive was to commandeer Samus's ship and escape). It is then absorbed by Samus, which fused her original power with her new Fusion Suit abilities and completes her. This new suit, the Omega Suit (although it is not actually called this in Metroid Fusion) finally gives back Samus' Ice Beam. Using her newly restored power, she defeats the Omega Metroid using the Ice Beam and clears the way. The computerized CO, with the help of the Etecoons and Dachoras, pilot Samus' ship to pick her up before the station crashes into SR388, eliminating any X Parasites on it (and therefore all the existing SA-X).