X-parasite

The X Parasites are a fictional species from the video game 'Metroid Fusion. In their natural form, the average X Parasite is a hovering, amoeboid creature that glows yellow, green, red or blue. Sometimes several such parasites will combine into a larger, more powerful form, known as a Core-X. The X Parasite mutates easily in order to adapt to new environments. X Parasites have the unique ability to infect, copy the DNA of, and kill another creature, then use the stolen DNA to create a new body with the same form and behavior as the previous host. Whereas normal X Parasites can only imitate weaker hosts, Core-X can also imitate much stronger ones. The X are also capable of combining DNA from various hosts to create a new creature with the abilities of the individual host forms. The X Parasites can also download and process electronic data organically. When threatened, an X Parasite will revert to its amoeboid form and is extremely difficult to harm, except by attack from a Metroid. X Parasites reproduce by asexual division.

Strictly speaking, the X are endoparasitoids rather than parasites. In a parasitic relationship, the host is not generally killed, whereas in a parasitoid relationship, the host is usually killed after the full development of the other organism, which is the case with the X.

One of the startling revelations in Metroid Fusion is the apparent intelligence of the X. Although first believed to be merely instinct driven mindless organisms, the X exhibit remarkable adaptation and even plot various traps to defeat Samus. Either by duplicating sentience or intelligence from the host bodies they infected, or having always been intelligent, by the time of the game they have achieved intelligence at least of human level. The X, realizing Samus' new vulnerability to cold, have some of the X mutate into blue X parasites, which have the X at an extremely cold temperature so as to severely damage Samus. the Varia Suit upgrade defends Samus from this problem, however the X also has the SA-X attempt many different ambushes in order to kill Samus. The X also mimic the dead corpse of a researcher in order to gain access to a particular computer terminal for their own purposes. The X also took the DNA from the frozen corpse of Ridley and created Ridley X. This variant of Ridley has all the attacks that the original Ridley had when he was still alive. This Core-X holds Samus' Screw Attack. When it is revealed that Federation Ships are on their way to retrieve the X, Samus knows that they will be no match for the X and will be used by the parasites to infect the entire universe. Indeed as Samus' A.I. companion Adam states, the intelligence of the X is nothing short of remarkable...and a little terrifying.

The X Parasites in the Metroid storyline
The X Parasites are such prolific breeders that on their home planet of SR388 they threatened to destroy the ecosystem. The Chozo stepped in and created the Metroids in order to keep the X Parasites' numbers in check. When series protagonist Samus Aran exterminated all of the Metroids on SR 388 in Metroid II: Return of Samus, the X Parasites' population quickly made a comeback. They provided the main antagonist role in Metroid Fusion, particularly in the form of the SA-X, an X mimic of Samus Aran and her Power Suit. As the X continued to menace the station, the Federation took an interest in the X. They ordered Samus' computer to confine her until Federation ships arrive. Samus, knowing that the X would overwhelm them and spread through the universe, set the station on a collision course with SR-388. By doing so, all of the X on the station and the planet would be destroyed. The SA-X tried to stop her, but was defeated.

SA-X


The SA-X is an X Parasite that copied Samus Aran's abilities on one of her trips to 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. 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 destucts; the second confronts Samus after she set the station on a course to hit the planet SR388, and later returns to try and defeat the Omega Metroid. The Omega Metroid defeats this SA-X which subsequently provides Samus with her coveted Ice Beam to defeat the Omege Metroid, in a similar fashion to the Hyper Beam from the ending of Super Metroid, which was used to defeat Motherbrain.

During the course of the game, Samus discovers a secret laboratory on the station that is cultivating Metroids, which the SA-X promptly destroys. 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 less 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 (which is thought to transform into a hornoad-like creature because Samus absorbed an X from a hornoad while still wearing her original power suit, thus making the X Parasite still have hornoad DNA in it.) 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). It is then absorbed by Samus, which fused with her original power with her new fusion suit abilities and completes her. This new suit, the Omega Suit, now colored in her trademark orange, yellow, and red, also 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).

Metroid Prime
It may be noted that after the Metroid Prime's essence is destroyed, the being left over resembles a core-X.