The Eight Octoliths are mysterious Alimbic artifacts of incredible power. They are the keys needed to activate the Alimbic Cannon, which is the only thing that can open the way to Gorea's prison, the Oubliette.
The Octoliths were created by the eight Alimbic Elders after sealing Gorea in the Eternity Void. They had been created to be the keys to the Alimbic Cannon, and contained the calculations and access codes needed to operate the cannon. After their creation, the Elders sealed themselves within the Octoliths and had them hidden in pocket dimensions, which were accessed by portals found on the stations and planets in the Alimbic Cluster.
The Alimbics knew someone might try to steal the Octoliths for personal gain, so they had devised ingenious security mechanisms to keep them safe. First, the portals to the Stronghold Voids they are kept in require three artifacts to activate, which are protected by a variety of difficult challenges. Second, the Strongholds themselves are guarded by powerful Alimbic security mecha, which come in two varieties.
Cretaphid: A mecha that resembles a large alien totem covered in eyes with a shining crystal on top. The eyes, depending on the version, fire either chemical lasers, heat-seeking plasma (not sure how THAT works) or both. After losing the eyes, the power core on top emerges to fire energy blasts. When the core appears, the Cretaphid can take direct damage.
Slench: A mecha that looks like a huge robotic eyeball. A Slench primarily attacks by using the wall-mounted turrets, which are powered by the mecha's three synapses. The Slench series utilizes Power Beams, Battlehammer Heavy Repeaters, Magmaul Magma Cannons and Judicator Freeze Guns (for versions 1., 2., 3, and 4., respectively). The Slench shields itself when attached to the wall, but the synapses are vulnerable to attack, with them being weak to their weapon's opposite from Version 2. onward. After disabling the synapses, the Slench detaches from the wall and attacks with its affinity weapon, charge attacks and rolling (depending on the version). Of course, the now-exposed eye is its main weak point.
The final defense mechanism is a countdown that starts when an Octolith has been taken. When the countdown starts, Samus will have to get to her gunship and flee the area or else she will be killed. During the countdown, enemies are in greater number, especially Psycho Bits, Voldrums (if any), Alimbic Turrets and a pack of Guardians or two.
- Metroid Prime Hunters (First appearance)