Fission Metroid

Fission Metroids are Phazon-mutated Metroids with the ability to split into two forms. Like all Metroids, they are energy-based lifeforms with a translucent upper body. They have claw-like spikes that protrude from the lower halves of their bodies which they use to latch onto prey, which are probably their equivalent of normal Metroid mandibles. When a Fission Metroid splits into two forms, it endows the new Metroids with invulnerability to most weaponry. However, the effect is unstable, so during the split the Fission Metroid remains vulnerable to one particular weapon fire. The vulnerability is likely random due to the chaotic nature of Phazon mutation. They also explode if they drain too much energy.

In the Phazon Core of the Impact Crater, there is an endless amount of Fission Metroids, that are rising up through the Red Phazon. They also appear all over the Phazon Mines Level 3 after killing Omega Pirate in the PAL version of Metroid Prime, as well as New Play Control! Metroid Prime and Metroid Prime Trilogy. Weak Fission Metroids appear in the Phazon Processing Center after the Omega Pirate's death in the PAL and Wii versions. These Fission Metroids will die if they touch one of the Phazon crystals in the room, get hit by Auto Defense Turret fire or reach a certain point in front of the Red Door leading to the Processing Center Access room. They also perish after a few shots, before they can even split. No other Fission Metroids in the game are this weak. The Fission Metroids' differences in strength in both mentioned areas may be attributed to the different types of Phazon located in each.

When Samus Aran battles Metroid Prime's Core form in the Metroid Prime Lair, Fission Metroids will sometimes spawn from the pools of Phazon it creates. There are two ways to kill a Fission Metroid without causing them to split: Power Bombs and the Phazon Beam. Fission Metroids, along with the mentioned core form of Metroid Prime, are the first of their species in the Metroid series to have become invulnerable to cold. Years later, the Galactic Federation would successfully reproduce this invulnerability to the Metroids located on the Bottle Ship.

Types
The four types of Metroids the Fission Metroid splits are:


 * Yellow Power Metroid: Vulnerable to the Power Beam.
 * Purple Wave Metroid: Vulnerable to the Wave Beam.
 * White Ice Metroid: Vulnerable to the Ice Beam. Fission Metroids start out in a phase that looks similar to this, yet when they split into an Ice Beam Fission Metroid, they take on a slightly blue hue instead of white.
 * Red Plasma Metroid: Vulnerable to the Plasma Beam.

All of them are vulnerable to Power Bombs (and regular Bombs) and the Phazon Beam.

Website
"Fission Metroids are mutant Metroids with the ability to split into two forms. This split endows the new creatures with invulnerability to most weaponry. This effect is unstable, though, so during the split the Fission Metroid remains vulnerable to one particular type of weapon fire. The vulnerability appears to be random, perhaps due to the chaotic nature of Phazon mutation.

''An energy-based life-form with a translucent upper body. Claw-like spikes protrude from the lower half of the creature, which it uses to latch onto its prey."''

Trivia

 * The images used for the Fission Metroid on Metroid.com are that of a Hunter Metroid.
 * A possible explanation for why Fission Metroids split is that Phazon produces Beta Rays.
 * Fission Metroids are hive creatures as they are spawned in the Impact Crater from bubbling portions of Red Phazon.