Quadraxis is giant spider-like robot, with four legs, and a giant brain inside its head.
Metroid Prime 2: Echoes
Quadraxis is one of the guardians, and presumably the most powerful that serves the Emperor Ing. It is a three phase boss fight that test most, if not all of Samus' skills, while at the same time dealing with the toxic atmosphere.
In the first phase, Samus has to shoot at all four of Quadraxis's legs while avoiding its spin attack, machine guns, and other attacks. After all four of its legs are destroyed, its body collapses to the ground, but its head disconnects itself from the body and tries to kill Samus.
In the second phase, Quadraxis's head tries to kill Samus, so Samus has to use the Echo Visor to sever all the Connections between Quadraxis's body and head. When the link is destroyed, Quadraxis will try to re-connect the links. It will also summon Dark Quad Robots to defend itself. When all the connections are destroyed, Quadraxis somehow is still active, which begins the third and final phase.
3rd & Final Phase
In the last phase, Samus must attack Quadraxis until it is stunned. When it is stunned, Samus morphs into a ball and uses Spider-Ball Track to jump onto Quadraxis. Samus then processes by bombing the head twice at very specific areas. After that areas are destroyed, Quadraxis is finally destroyed and granting Samus the Annihilator Beam.