The Phantom Star Brigade is introduced in the final battle, when Echidna Pallas is forced to send them to the battlefield, since almost every Apostle has been defeated. She orders them to deal with Sven Vollfield and Eve, two of the main protagonists, as well as the Chrono Numbers IV, VII, VIII and X, but they all end up defeated, most of them even being destroyed.The Phantom Star Brigade only actually appears in the manga. Only two of them are seen in the anime adaptation and for a few seconds. They are seen attacking Train Heartnet, the primary protagonist, but the fight is never displayed.
Each soldier of the Brigade was fused with all sort of heavy weaponry and turned into a cyborg. They are all ruthless and sadistic assassins, (sometimes to the point of psychosis) whose only goal in life is to fight. The Cyborgs' robotic body grants them strength, speed and durability way beyond human level, and protects them against bullets and most regular attacks or weapons.They are also equipped with sensors that vastly enhance their perception. They are very powerful and dangerous but exceedingly overconfident, considering themselves superior to every opponent they may face, should it be a Chrono Number. In spite of them being a force to be reckoned with, such claims are ultimately proven wrong.
The Flying Cyborg
One of the two cyborgs tasked to fight the protagonists. He is the only cyborg whose face is (partially) revealed and he is often seen yelling with joy with his mouth wide open. Among the entire Phantom Star Brigade, he is the most deranged and the most sadistic.
He is able to fly thanks to a jetpack-like system on his back and feet, and to separate his torso from his lower body while still controlling both. He is highly fast and is armed with retractable blades, machine guns and flamethrower in his arms and with a rocket launcher in his belly.
He engages an aerial battle against Eve (who can fly by sprouting angel-like winds from her back) and gains the upper hand for a short while by separating his body and attacking her from two sides at the same time. However, she cuts his legs into tiny pieces before asking him if he chose to become a cyborg. Upon learning the truth, she answers "I have no reasons to go easy on you." Eve then grabs him by the arm and violently smashes him to the ground, disabling him. He likely survived, given that Eve would never bring herself to kill anyone, should it be a demented cyborg, also given that he later is seen twitching on the ground.
The Golem Cyborg
The second cyborg tasked to fight the protagonists. The Golem is a huge and massively built cyborg, with his entire body filled with countless Gatling guns of variable size. He has also many rocket launchers on his back and enormous physical strength. He seems to have little patience and to care very little about everything his enemy might say.
Echidna sends him to fight Sven but the bulky warrior is unable to land a single hit on the bounty hunter, even when firing with all of his Gatling guns at the same time. This being due to Sven's special power: the Grasper Eye, which enables him to control the speed of everything he sees, with which he slows down every bullet easily avoiding them all.
Despite this disadvantage, the Golem is impervious to any bullet, and if struck by a grenade or a powerful attack, all the ammunitions inside him would ignite resulting in an explosion that would completely obliterate the bridge they are fighting on. Sven ends up using a "Water Cut": a highly pressurized water jet able to cut through almost anything, slicing the cyborg in half. The Golem's useless body is later seen twitching, hinting that he may have survived.
The Snail Cyborg
The Snail Cyborg is extremely cocky, and he cannot stand when his enemy is not afraid of him. He has a huge metallic shell integrated to his back; inside which he can hide to be protected from almost every possible attack or perform dangerous rollout attacks at variable speed.
He attacks Jenos Hazard, the Chrono Number VII, getting angry since Jenos never loses his calm. Eventually, Jenos makes a pillar collapse on him, which stops his rolling attack and causes him to exit his shell, wide open for the Number's attack. Jenos ultimately takes pity on the fanatic cyborg and decides to spare his life.
The Snake Cyborg
This cyborg is never seen fighting, so his weaponry remains unknown. It can be guessed that he fights with his metallic tail, which is likely sharp as a blade and sturdy as a shield. He might also throw acid or poison at his enemy.
The Four-armed Cyborg
The four-armed Cyborg is as big and bulky as the Golem and possibly equally strong. He is never seen fighting and as such, his weaponry is never revealed. He is apparently extremely (over)confident in his abilities, as he challenges Kranz Maduke and Baldorias Fanghini, the Chrono Numbers IV and VIII, on his own. Unfortunately for him, they are two merciless fighters, even more bloodthirsty than the Phantom Star Brigade itself. As we can see on the picture, the confrontation obviously did not go well for him.