The Plax were operating in the deserts of Shanazar aboard a drilling rig, mining for a material called Magnaz that could power their factory and produce more of themselves. Their drilling operation was causing several earthquakes which had destroyed a number of surrounding villages. Sonic the Hedgehog - who was stranded on Shanazar at the time - went into the desert to investigate the quakes. He found the Plax and their drilling platform and demanded that they stop drilling. The Plax were unconcerned by the damage they had been causing and warned Sonic to leave, but the hedgehog attacked. His attacks were futile as the Plax's plastic bodies were so malleable and they could reform themselves easily. Sonic realised he could not fight the creatures and their technology was too complex for him to shut down, so he used his super-speed to reverse the rotation of the drill. The maneuver worked and the rig was torn apart. With their facility destroyed, the Plax decided upon a new objective: to destroy Sonic the Hedgehog.
The Plax's opportunity for revenge would come some weeks after the Microverse was merged with Mobius. When the Plax arrived on Mobius, they approached the psychotic Doctor Robotnik and offered their service to him, believing him to be their legendary Great Destroyer who would bring about the annihilation of all life. They planted a machine on Easter Island on Earth that siphoned off the planet's life energy, and did the same on Mobius as well. They also constructed several robotic monsters made up of Microbots to defend these devices. Robotnik was connected directly to their machine on Mobius and the life energy of both planets was pumped straight into his body. When the Freedom Fighters discovered the source of the anti-life anomaly, the Plax were on hand to stop them. The heroes tried to blast them, melt them, blend them together, but nothing was effective. Grimer intervened and told the Plax that Robotnik planned to kill them along with everything else. The Plax scanned Grimer's mind and realised he was telling the truth. With this revelation, the Plax retreated to their base to kill Robotnik. However, Robotnik had already absorbed so much energy from Mobius and Earth and sensed the Plax's betrayal. He unleashed powerful beams of energy which struck all of the Plax, vapourizing them all.
Physically, all the individual Plax look identical: squat humanoid bodies with green skin; large, bulbous heads with narrow yellow eyes and lipless triangular mouthes containing straw-like tongues; long, double-elbowed arms with three-fingered hands and short legs with three-toed feet. The Plax appear to all be wearing grey jumpsuits, but the clothing is just another part of them.
The Plax possess a hive-mind intelligence, all of them are united and think the exact same things. When they set themselves an objective, they will focus on nothing else unless interrupted by outside forces. They are also capable of scanning the thoughts of other living minds, but whether they have any other psychic abilities beyond this is unknown.
Physically, the Plax are very strong. Ordinary attacks will do no damage to them and even unusual attacks and heavy weapons seem to have minimal effect. If any of them are torn apart, they can simply reform themselves. They can also blend together and alter their consistency, becoming as hard or soft as they need to be. The only kind of attack that seems to have had any effect on the Plax is a focused projection of energy. When Dr. Robotnik absorbed the life energy of Mobius and Earth, he fired beams of it from his eyes which seemed to home in on the Plax and vapourize them one by one. The Plax were completely wiped out by this attack.