Core-X are large X Parasites that have incorporated into themselves either an important ability from their victims or one of Samus Aran's lost power-ups. They take the form of a boss and, upon defeat, discard the host body and reveal their natural form.
Core-X are surrounded by a tough membrane covered in spikes. To break the shell, Samus has to fire Missiles at it. Once Samus has damaged it, the shell will flash for a few seconds, giving it temporary invincibility; on Easy Mode in the Japanese version of the game, Core-X are invincible for only half as long. As it takes more damage, it changes color from green to yellow to red. If Samus uses any Beam or Screw Attack on a Core-X while it is not flashing, Yellow and Green X Parasites will fly out of it; this may be a defense mechanism to launch the pure form of X so that it may infest whatever creature is attacking it. Since Samus is part-Metroid throughout most of the story's events, this defense mechanism becomes an advantage to her since she can absorb X to replenish her Energy and Missile Ammo.
A Core-X was once a regular X Parasite, but it was able to find a host with such power that it gained a hard shell and the ability to produce more X. For example, a normal yellow X infected Samus, but a Core-X is revealed when the SA-X is defeated. The power-up that Samus recovers from a Core-X often belonged to the host it previously infected, and is used greatly by the parasite in its battle with Samus. For instance, Samus gets the Morph Ball from Arachnus, who rolls up into a ball; the Space Jump from Yakuza, whose head continuously jumps; the Gravity Suit from Nightmare, who controls gravity; the Speed Booster from Serris, who moves at incredible speeds; the High Jump Boots from Zazabi, who leaps extremely high; the Storm Missile from Escue, who rapidly fires multiple homing projectiles; and the Cross Bomb from Golzuna, who releases energy bombs that detonate in cardinal patterns.
As Metroid Fusion's story develops, the computerized Adam Malkovich warns Samus about the X evolving and growing stronger to the point where some of them are becoming resistant to her weapons. This is evidenced by the increasing number of Missiles it takes to defeat each newly encountered Core-X, with the very first Core-X (Arachnus) only requiring three Missiles and the next Core-X (Zazabi) requiring four, needing an additional missile to change it from blue to yellow in color. By the end of the mission, it finally plateaus at six Super Missiles to defeat a single Core-X, which will take two missiles to change phase/color. However, in Metroid Dread, the two Core-X that Samus faces have the same health and are additionally vulnerable to charged Plasma Beam shots. The protective membrane can also be destroyed instantly with a single salvo from the Storm Missile or with a single Shinespark.
The SA-X's Core-X replenishes all energy and ammunition, while all others in Fusion restore 4 Energy Tanks, 50 Missiles, and 10 Power Bombs. Core-X do not restore any energy or ammo in Dread.
There are two types of Core-X. The simplest to defeat is the normal Core-X that moves at high speeds around the arena trying to tackle Samus with its spiny exterior. This Core-X simply requires Samus to shoot it with Missiles until the shell cracks off to allow the absorption of the X inside. This variant can also grow to gargantuan sizes if downloading suit upgrades directly, as well as spawn miniature variants of itself.
The second variant is one that holds a beam weapon, officially identified as a Beam Core-X. This Core-X that has complete protection from any weapon, including Missiles. While this kind of Core-X moves at slower speeds than a standard Core-X, it is also equipped with a long-range attack. Because they hold beam upgrades for Samus, it's not surprising that the Core-X would try to use the beam's power, hence their designation as Beam Core-X. In battle, the Core-X will open an eye-like part of its shell and begin charging an energy weapon, just as Samus would with her Charge Beam; each Core-X uses the weapon that it holds (for example, the Core-X that appears after the defeat of the SA-X uses the Ice Beam). The Core-X will then fire the beam after it is fully charged. The charging period is the only time that the Core-X is open for attack, and only the "eye" can be damaged. The beam will be fired prematurely if the Core-X is hit, so it is recommended that Samus jumps as soon as she fires a Missile.
In total, Samus encounters 12 Core-X during her mission aboard the B.S.L Research Station (7 standard Core-X and 5 Beam Core-X). During her mission to ZDR, she encounters 3 Core-X, none of which are Beam Core-X.
List of creatures containing standard Core-X
- Arachnus: Morph Ball
- Zazabi: High Jump Boots/Jumpball
- Serris: Speed Booster
- Barrier Core-X: Varia Suit
- Yakuza: Space Jump
- Nightmare: Gravity Suit
- Neo-Ridley: Screw Attack
- Escue: Storm Missile
- Golzuna: Cross Bomb
- Experiment No. Z-57
Experiment No. Z-57's Core-X is not absorbed by Samus as it is knocked off a ledge and plunges into lava. What ability it would have provided is unknown.
List of creatures containing Beam Core-X
- Elephant Bird: Charge Beam
- Scientist: Wide Beam
- Nettori: Plasma Beam
- Security Robot B.O.X.: Wave Beam
- SA-X: Ice Beam and "Omega Suit"
Metroid Fusion manual
- ABSORB CORE-X (pg. 29)
- "The other method for reclaiming lost abilities is to absorb a mega-sized X parasite known as a Core-X. The image here is one of several types of these dangerous creatures. The abilities of the Core-X parasites differ from type to type, but the thick thorny membrane that encases them is a common feature. This tough casing must be ruptured by a powerful attack, such as a Missile blast, to render the core vulnerable to absorption. Some of the Core-X parasites are incredibly powerful - engage them with caution. A Core-X will release X parasites when shot with beam weapons. Use this to your advantage when low on missiles or energy."
- The form Metroid Prime takes upon being vanquished in Metroid Prime resembles that of a Core-X.
- The Core-X without its shell resembles an adenovirus, a type of virus with an icosahedral capsid structure.
- The Plasma Beam will not phase through a Core-X while it is flashing during its invincibility time.
- Despite being a powerful host and the final boss of Metroid Dread, Raven Beak X appears to contain an ordinary X Parasite instead of a Core-X, albeit one of an unusual color not seen in other X.
- ^ Looygi Bros. "11 Cool Details in Metroid Dread (Part 6)". YouTube. January 16, 2022. Retrieved January 18, 2022.
- ^ Looygi Bros. "12 Cool Details in Metroid Dread (Part 9)". YouTube. February 1, 2022. Retrieved February 2, 2022.
- ^ Metroid Prime and Metroid Fusion: Prima's Official Strategy Guide pages 84, 124, and 135