SA-X

SA-X (also known as Samus Aran X or Samex) is the tenth boss Samus faces aboard the Biologic Space Laboratories research station in Metroid Fusion.

Biography
The SA-X is an X Parasite mimicking Samus. After Samus's first encounter with the X on SR388, her Power Suit was infected by the parasites. The Galactic Federation removed the suit surgically and sent the pieces to the BSL resarch station's Quarantine Bay. Once there, the infected suit parts transformed into an X resembling Samus. The SA-X was able to use a Power Bomb to escape the Quarantine Bay, which caused the capsules containing all the X to break open, showing the SA-X started the X infestation.

From then on, the SA-X roamed the station. It eventually learned that Samus was aboard the station and set out to destroy her. With the use of the Ice Beam, Samus stands no chance against the SA-X due to the Metroid vaccine. Thus, whenever Samus encounters the SA-X, she must hide or run from it, which happens on more than three occasions. One of these occasions shows the SA-X fighting Metroids in the restricted zone, though they overpower it. Apparently, the SA-X had released the infant Metroids, caused the zone to be locked down, and eventually causing it to fall away from the research station and explode, with Samus barely escaping.

After that incident, Adam tells Samus that there is more than one SA-X and that they asexually reproduce and that the Galactic Federation has taken an interest in the SA-X and believe that it has strong potential. The computer goes on to tell Samus that the Federation does not expect Samus's help, which is why they stopped sending her support data.

Once the computer updates to Adam Malkovich's personality, Adam tells Samus to go the Operations Room and adjust the station's orbit path to intercept SR388. Once Samus reaches the Operations Room, she encounters an SA-X and must finally battle it.

The battle
The SA-X uses the Ice Beam and Screw Attack against Samus. Only the Charge Beam will damage it; Super Missiles will not work. As the SA-X takes more damage, it starts to look distorted and once it can not take any more damage, kneels on the floor.

Once Samus approaches the SA-X, it transforms into a gigantic beast, a sort of mutant hybrid Hornoad like creature, which was the host of the X before it infected Samus in the first place. It will jump around the room and try to stomp on Samus (there is a safe spot during this stage of the fight; if Samus is on the ledge in front of the Operations Room door, she can shoot down through the floor, but the SA-X can't jump high enough to reach her). Again, only using the Charge Beam will damage it. Once this form has been defeated, it will transform into a Hard Core-X. However, once Samus defeats the Hard Core-X, the X inside floats away from Samus.

The end
Once Samus reaches the Docking Bay where her gunship should be, she instead encounters an Omega Metroid. The Omega Metroid attacks Samus, leaving her with an ounce of her life left. Just as the Omega Metroid is about to deal the finishing blow, the X that floated away from Samus after defeating the SA-X appeared and transformed back into its original SA-X form. It then used the Ice Beam against the Metroid, causing it to back away from Samus. Once the Metroid reached the end of the room, it retaliated and attacked the SA-X, causing it to bounce back in front of Samus. It then transformed back into an X, allowing Samus to infuse it. She then gained the Ice Beam back and was wearing the Omega Fusion Suit.

Once Samus defeated the Omega Metroid and the BSL research station crashed into SR388, all the SA-X' were supposedly destroyed.