SA-X

The SA-X (short for Samus Aran-X) was the main antagonist of Metroid Fusion and the eleventh boss Samus faces on the Biologic Space Laboratories research station.

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 surgically removed infected portions of her suit and sent the pieces to the Biologic Space Laboratories research station's Quarantine Bay. Once there, the X inside the infected suit parts seemingly combined and transformed into a copy of Samus in her standard Varia Suit (it should be noted in SA-X's first closeup, the helmet and upper torso seem to be a shade of purple, and her eyes appear to be white, with no visible pupils). The SA-X used a Power Bomb to escape the Quarantine Bay, breaching the capsules containing X-infected specimens from SR388 and starting the mass infestation.

From then on, the SA-X roamed the station, occasionally crossing paths with Samus and attacking her on sight. As it had the use of the Ice Beam, Samus originally stood no chance against it because the Metroid vaccine had left her with an extreme vulnerability to cold. Thus, whenever Samus encountered the SA-X, she would have to hide or run from it.

The copy was first seen when Samus was traveling to Sector 1 to try and stop the X infestation from spreading. As Samus went down the Main Elevator, the SA-X blew up a wall of the elevator room, walked into the room, and paused for a few moments; it is here that a close-up of its face could be seen. The SA-X then jumped over the elevator shaft, destroyed the room's hatch with a Super Missile, and left the room through the destroyed hatchway. When Samus reaches Sector 1, the computer informs her that some "unknown agent" had severely damaged the Main Elevator and disabled it for the time being.

Upon Samus' arrival in Sector 2, the computer briefed her about the SA-X, informing her that it disabled the Main Elevator, told her about its abilities and to avoid it at all costs. The second encounter occurred shortly afterward, which was after Samus downloaded the Bomb data. As soon as Samus left the Data Room, an explosion shook the surrounding area, immediately after which the SA-X's footsteps could be heard fading away into the distance. When Samus dropped down to the lower part of the room, she discovered that the hatch she had come through had been badly damaged and rendered totally inoperable.

Samus' first physical encounter with the SA-X also occurred in Sector 2, shortly after the defeat of Zazabi. Attempting to return to the Navigation Room, Samus discovered another damaged and completely impassable hatchway. Using her Bombs, she was able to open a hole in the floor nearby and dropped into a room with two sections. The SA-X was in the bottom section, but it soon left the room.

After leaving Sector 2, Samus wondered about the SA-X being a mindless creature.

The next encounter, this time in Sector 6, occurred when Samus discovered a wall of Power Bomb Blocks that she could not pass, as she had not yet recovered her Power Bombs. The SA-X entered the room almost immediately afterward, forcing Samus to hide in a passageway under the floor; after walking to the wall, it then used a Power Bomb of its own to destroy both the wall and a significant portion of the floor. It then jumped down the next area and exited the room.

The third actual encounter took place in Sector 5 after Samus had downloaded the Power Bomb data. While using Power Bombs to get around blockages created by the X, Samus entered a portion of the sector she had not previously explored. Almost immediately afterward, the SA-X suddenly entered the room right behind her. To escape, Samus had to jump over a pillar and use Bombs or a Power Bomb to find a secret passage in the wall behind it. Unfortunately, if Samus set off a Power Bomb, the explosion would destroy the pillar behind her, revealing her position to the SA-X and alerting it to her presence; it would then run over to the wall and fire Ice Beam and Wave Beam shots until Samus left the room.

The SA-X showed up once again in Sector 2 shortly after Samus activated the Auxiliary Power Station. While traveling towards the source of the vegetation choking the Central Reactor Core, Samus dropped into a large chamber only to discover that the SA-X was there waiting for her. As she still lacked a way to damage it, Samus was left with no choice but to run from the SA-X until she could reach a safe hiding place, though she could slow it down by hitting it with Ice Missiles.

When Samus' navigation computer requested that Samus destroy B.O.X., he warned Samus that the SA-X was hunting for her in Sector 6 and ordered her to leave the sector immediately after defeating B.O.X. After destroying B.O.X., she reached the Restricted Laboratory and discovered the Federation's secret Metroid breeding project. Following the sound of the explosions rocking the lab, she found the SA-X attacking infant Metroids, though it was quickly overpowered and overwhelmed. However, the SA-X's assault had activated the emergency fail-safes—moments after Samus escaped, the Restricted Area was jettisoned from the research station and exploded. Samus believed that the X mimic was gone for good.

However, her feelings of victory were short-lived. After the incident, Samus' navigation computer told her that there were no fewer than 10 SA-X because the X reproduce asexually. Shortly after, the Galactic Federation had taken an interest in the SA-X, believing it to have strong potential as a bioweapon The computer went on to tell Samus that the Federation did not expect her help in containing the SA-X, which is why they had stopped sending her support data., and tried to detain Samus in the room until she accidentally called the computer "Adam".

Once the computer was revealed to have Adam Malkovich's personality, he told Samus to go to the Operations Room and adjust the station's orbit path to intercept SR388, effectively wiping out the X Parasites for good. Just as Samus reached the Operations Room, the SA-X returned and ambushed her in an attempt to stop her from destroying the station. By this time, Samus had recovered almost all of her lost abilities, including those she needed to damage the SA-X. Therefore, she was able to finally confront her doppelgänger, and after a fierce struggle, Samus emerged victorious. However, the SA-X, in form of an unprotected Core-X, escapes before being absorbed by Samus.

As Samus tries to escape the station, an Omega Metroid blocks her path and strikes her down. The very same SA-X appeared and attacked the Metroid, but the predator hit the SA-X with an exact strike that had immobilized Samus, reverting it back to a Core-X. This allowed Samus to absorb the Core-X, which in turn allowed Samus to recover her energy completely and regain the Ice Beam and acquire the Omega Suit, and defeated the Omega Metroid. Why the SA-X helped Samus at this point is unknown.

Artificial intelligence
Despite having Samus's powers and, according to Adam, a high intellect, the SA-X is infamous for its incredibly poor artificial intelligence coding. There are various holes and ledges that Samus can hide on or in that will cause SA-X to endlessly run and jump back and forth without hitting Samus, sometimes even if she is within easy reach.

In one example, in the first encounter of Sector 2, if Samus attracts attention, it will chase after her, but if she climbs up the hole she came through, the SA-X will run to the wall, lose interest in the chase and walk peacefully across the room to leave.

In another example, in Sector 6, the SA-X Power Bombs a floor above a Morph Ball tunnel, revealing Samus if she isn't quick enough; if Samus rolls into the intact part of the tunnel on the right side (the part where she came in through) and is seen doing so, it will Screw Attack and Space Jump to the top part and back down to the bottom in an endless cycle as long as she stays there.

Also in the same scene, if Samus falls into the Fake Block chamber and hangs there while the SA-X is alerted, it will drop down to the lowest part of the room and constantly run back and forth across the room.

Additionally, in the next room, when Samus climbs into the Morph Ball shaft, the SA-X, like before, will constantly run back and forth.

When hiding from the SA-X in Sector 5, if Samus fires any projectile or drops a Bomb behind the pillar (without destroying it) when the doppelganger turns to leave, the SA-X will turn around as if it had heard something and walk back to the pillar, but it does not extensively search the room or even shoot its Wave Beam at the pillar and will shortly lose its interest before leaving unless its attention is attracted again. This goes on until Samus stops or she reveals herself to her opponent. This also occurs in the second encounter of Sector 2, at the very last room, although it stays near the door.

In the second encounter of Sector 2, if Samus is to crouch in the one-square-wide space after the third shutter in the room before the aforementioned pillar, the SA-X will jump over Samus from atop the pillar to the ground and back with no end until Samus leaves the area. The SA-X even continues this regardless of what Samus is actually doing in the space, whether she is in Ball form, crouching, standing, shooting beams or missiles in any direction, or even Bomb Jumping (up to how tall Samus would be standing in the space) to taunt the SA-X. If Samus jumps in the same encounter, the SA-X turns around and heads to the edge of the slope. If a Power Bomb is dropped, it shoots at where it thinks Samus is, repeatedly.

Notably in Sectors 6, 5, and the second encounter of 2, if Samus stands on top of one of the various pillars she uses to hide from SA-X or goes into a narrow Morph Ball tunnel but stays close to the edge her opponent, unable to comprehend the fact that it needs to jump higher to reach Samus or aim and fire at her, will try to Screw Attack up to her but will always fall short, and it will keep trying the same method until Samus leaves its sight.

Despite its horrid AI coding, the SA-X is truly intelligent... story-wise anyway. For instance, the SA-X destroyed the Quarantine Bay with a Power Bomb in order to escape. It also destroyed numerous Data Rooms and/or as much access to them as possible in an attempt to prevent Samus from regaining her abilities. Additionally, the SA-X predicted her movements: it was waiting for her in Sector 2 as it knew she was going to try to destroy the Nettori as well as following her into Sector 6, the Restricted Laboratory and the Operations Deck. If Samus hung on a ledge out of the SA-X's reach, it will fire a Super Missile in order to dislodge its enemy due to the rumble created by said Missile. Finally, it knew the most efficient way to destroy a Metroid; freeze it with the Ice Beam then shatter it with a Super Missile. This is because the X are able to absorb knowledge from their victims, in this case the SA-X has Samus' knowledge of how to eliminate Metroids.

Abilities
During the course of the game, the SA-X demonstrates the following abilities of Samus's Power Suit:
 * Super Missile
 * Ice Beam
 * Plasma Beam
 * Wave Beam
 * Spazer Beam
 * Morph Ball
 * Power Bomb
 * Space Jump
 * Screw Attack

The battle
The SA-X uses the Ice Beam, Screw Attack, and sometimes Super Missiles (it fires them when Samus hangs from a ledge out of reach) against Samus. Only the Charge Beam can damage it—Samus can temporarily freeze it with an Ice Missile, but it causes no actual damage. The SA-X has a tendency to go into a Screw Attack as a counter-attack whenever Samus lands a blow; if Samus tries somersaulting into it with her own Screw Attack, both will take damage. As the SA-X takes more damage, it begins to look more and more distorted; once it cannot take any more damage, it falls to its knees (much like Samus herself at the end of Super Metroid).

When the SA-X kneels down, it stops fighting. When Samus approaches, though, it transforms into a gigantic beast, that appears to be a sort of mutated Hornoad-like creature. One possible explanation for this form is that it was a fusion of every host the SA-X had previously infected, namely a Hornoad and Samus herself; this would explain why the form looks like a giant mutated Hornoad with a swollen Arm Cannon on one of its arms; it also retains the suit's visor in the form of one large visor above its mouth and multiple, smaller visors above the largest one and a coloring pattern similar to that of the suit. Despite still having a type of Arm Cannon, the SA-X then jumps around the room trying to stomp on Samus. Ultimately, this tactic proves much less effective than when the SA-X was only mimicking Samus, as there are a couple of ways for Samus to avoid damage: if Samus stands on the upper ledge in front of the Operations Room door, she can use the Wave Beam to shoot down through the floor, but the SA-X can't jump high enough to reach her. Alternatively, Samus can use the Screw Attack to somersault right through the SA-X; this won't hurt the SA-X, but Samus won't take any damage, either. In order to damage the SA-X, Samus must once again use the Charge Beam.

Once the mutated form is defeated, the SA-X reverts to a Core-X and attempts to both fly into Samus and hit her with the Ice Beam. Once Samus defeats the Core-X, the X inside retreats out of reach, eventually phasing through a wall and escaping.

The conclusion
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 only one unit of her energy left. Just as the Omega Metroid is about to deal the finishing blow, the SA-X that fled after Samus defeated it reappears and transforms back into its Varia Suit form. It then uses its Ice Beam against the Omega Metroid, causing it to back away from Samus. Once the Metroid reaches the end of the room, it retaliates and attacks the SA-X, draining what little vitality it had recovered after its battle with Samus. The SA-X then reverts to its X form and allows Samus to absorb it, completely restoring her energy and granting her both the Ice Beam and the Omega Suit. Once Samus defeats the Omega Metroid, her gunship returns, allowing her to escape. The BSL station then crashes into SR388. All of the remaining SA-X were supposedly destroyed along with the planet and the rest of their kind.

Why the SA-X seems to assist Samus is unclear; it is likely that it saw two threats: Samus, a being with little Metroid DNA, and the full-blooded, incredibly powerful Omega Metroid, and thus the SA-X then attacked the greater threat; if this is the case, then it probably intended to finish off Samus after the Omega Metroid. The ending bears similarity to the ending of the previously released game Super Metroid, in which the baby, after believing Samus to be its "mother", sacrifices itself to save her from Mother Brain. It is possible, but less likely that after being defeated by Samus the SA-X grew to respect her as an admirable adversary and therefore protected her.

Official website
"While exploring SR388, Samus was infected by an X Parasite. Samus survived the infection, but so did the parasite. Now an exact replica of Samus at full power, SA-X may be the most potent foe Samus has ever faced."

Trivia

 * While the X were capable of infecting the organic parts of the Power Suit, it was already believed that they could not replicate robotics and technology; thus, the technology and metal shell of the suit should not have been replicated. Yet it is known that the SA-X had multiplied at least 10 times over the course of Fusion, thus raising the question as to how the SA-X copies obtained the technological aspects of Samus' suit. A logical explanation is that the suit was recreated by the X while retaining all of the suit's abilities, presumably through data in the biological components. When Samus is fighting the SA-X, it begins to look distorted as the fight goes on and mutates into a large creature near the end of the battle, which also suggests that the appearance of the suit was affected by the SA-X's will and that it is not actually wearing a real suit at all. This is likely to be the case with several other X forms which display inorganic components, among them Nightmare, the scientist, and the Zombie researchers. Alternatively, it is possible that the suit is 100% organic or connected to Samus' genome in some way. Samus states herself that her Power Suit was truly connected to her nervous system. This explains why the SA-X were able to grow the Power Suit parts like they did.
 * The SA-X knew the preferred tactic to kill Metroids (as it had acquired the knowledge from its victim) and used it against Samus Aran prior to her acquiring the Varia Suit: the SA-X would first freeze her and then shoot a Super Missile.
 * Despite this, the SA-X never used this combination of attacks against the Infant Metroids located in the Restricted Laboratory and instead fired concussive weapons in an erratic manner. This may have been because it was being swarmed at the time by the Metroids.


 * The fact that the Federation wanted to capture the SA-X for military use despite its obvious malicious intent is similar to the theme of the Alien series, where the corrupt Weyland-Yutani company wants to use the malicious Aliens as bio-weapons.
 * In trailers for Fusion, the SA-X's sprites appear to be directly based on Super Metroid ' s Varia Suit sprites.
 * The SA-X can be temporarily frozen (though only for a very few moments) if Samus fires Ice Missiles at it, buying her more time to escape.
 * Similarly to how Metroids take heavy damage from missiles when frozen, the SA-X takes double damage when frozen, though it requires some good timing and taking a short distance.
 * The SA-X is one of two beings in the series that is known to have Samus' DNA, the other being Dark Samus. Both are also main antagonists in the series. Unlike Dark Samus, who has been known to be capable of compassion, hatred and amusement, the SA-X only displays hatred and surprise and even a little mercy for Samus at the end of fusion.*Despite Samus' Screw Attack resembling something akin to a buzzsaw after absorbing the ability from Neo-Ridley, the SA-X uses the green Screw Attack present in Super Metroid. Additionally, the Screw Attack sprites may depict the SA-X in the Gravity Suit (though it wears the Varia Suit), as evidenced by the purple hue.
 * The SA-X is referred to using genderless pronouns, even though it could be assumed female due to containing Samus' DNA (this was the case with Dark Samus). It is, however, referred to as a male in one instance in Metroid Prime and Metroid Fusion: Prima's Official Strategy Guide. It could be considered female due to the fact that it shares Samus' DNA.
 * Despite Adam stating there were no fewer than ten SA-X in existence, none are encountered if the station is explored later in the game. Samus will only come across the one she faces as a boss and the one fighting Metroids in the Restricted Zone.
 * During the final stage of the SA-X fight, if Samus deals the finishing blow to the Hornoad-like creature far enough away, it will stand in one place and emit the same sound repeatedly until Samus stands close enough to it. Upon Samus' approach, it will slouch and transform into a Core-X.
 * The SA-X is one of the four bosses who necessarily engages Samus more than twice over the course of the game, the others being Dark Samus in Metroid Prime 2: Echoes, Ridley in Metroid Prime 3: Corruption, and the Rhedogian in Metroid: Other M.