Omega Metroid

The Omega Metroid is the fifth and final stage of a typical Metroid's life cycle (Not counting the Metroid Queen). The Omega Metroid is is about twice the height of a human with exoskeleton that leaves only a small area of soft membrane at the ribcage exposed. Like the previous Zeta stage, the Omega Metroid has a leech-like mouth, bipedal structure, a tail, and clawed limbs.

Samus Aran encountered the Omega Metroids during her mission to SR388. She would later fight another Omega Metroid created by Galactic Federation experiments on the Biologic Space Laboratories research station. It is never fully explained as to why the Omega Metroid is in the docking bay while the BSL Space Station is being propelled towards SR388, however it is likely that it escaped from the Research Lab before it was jettisoned from the main space station and developed. Indeed, several Metroid shells can be located around Sector 1 (SRX), each one being left behind as the Omega Metroid evolved.

Samus was not powerful enough to defeat the Metroid, however with the assistance of the SA-X and its Ice Beam ability, the Omega Metroid was defeated.

Inconsistencies
The Omega Metroids differ significantly in structure and behavior between Metroid II and Metroid Fusion. In Metroid II, the Omega Metroids are only about 150% the size of Samus, while in Metroid Fusion they are in fact much larger. At the same time, the Metroid II Omega Metroids are also able to levitate, take damage from normal Missiles, and were immune to the Ice Beam. But the Metroid Fusion Omega Metroid is not able to levitate, is immune to Ice Missiles, and is only weak against the Ice Beam. Possibly the cloned Omega Metroid was not a perfect copy of an original, or the Metroid Fusion developers purposely changed its specifications.

Battle Tactics (Metroid II)
The Omega Metroids are quite a bit slower than their Zeta counterparts, but can deal an enormous amount of damage. They maintain the basic structure of their last forms, and at the same time keep the same weaknesses; shoot them either in the stomach or back. Although it is highly recommended to shoot them in the back, because you will both deal triple damage and be in a safer position to fire. Omega Metroids typically levitate around while periodically pausing for a moment. When they're not causing damage by coming into contact with you, they spit projectiles from their mouths. Without utilizing their weakness, they require 40 missiles to bring down.

Battle Tactics (Metroid Fusion)
Starting out in the battle, you will not be able to cause any damage to the Omega Metroid. It will swipe you once with its claw, simultaneously reducing your energy to one point and knocking you to the back of the battle field. An SA-X will come to join the fight by shooting the Ice Beam into the creature's torso, the weakpoint. But the SA-X is killed on the spot almost immediately, and will float around as an X Parasite without form. This is your cue to absorb it. You will gain the Ice Beam, the ability necessary to defeat the Omega Metroid.

The Omega Metroid slowly creeps toward the left side of the docking bay throughout the duration of the battle in order to swipe you with its claw. The Ice Beam will drive the creature backwards in order to avoid this (This battle's mechanics are slightly similar to the battle with Crocomire in Super Metroid). If the creature manages to swipe you with its claw if you wander too close, you will be knocked to your knees to the end of the docking bay exactly as you were in the beginning of the battle. When this happens, it wastes your escape time and puts you in a vulnerable position. To prevent this from happening, use a bombing run technique: Charge the Ice Beam far from its reach, run towards the Omega Metroid and fire it angled upwards into its torso. Run back to the original position before it can swipe you and repeat until its death.