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. 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.

In the third room of the Impact Crater they respawn after you defeat them, so they are unlimited. They also appear all over Phazon Mines Level 3 after killing Omega Pirate in the PAL version of the game.

When Samus Aran battles Metroid Prime, 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, and they are Power Bombs and the Phazon Beam.

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


 * Power Metroid: Vulnerable to the Power Beam.
 * Wave Metroid: Vulnerable to the Wave Beam.
 * Ice Metroid: Vulnerable to the Ice Beam.
 * Plasma Metroid: Vulnerable to the Plasma Beam.

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