Zyx came to earth for one purpose, to have fun. Sick of Zerox's countless rules he wanted to cut loose for once and chose the earth as where to do it. Unable to stop his incredible power he could not be stopped until Phantom girl was able to convince Zerox's president and head sorcerer to intervene and take the boy home to be punished by having his powers stripped
A former opponent of the Legion, Zyx had his powers removed and appeared to the Legion and said that his homeworld Zarok had been conquered by the evil sorcerer Mordru.
As they went to Zerox to investigate, Zyx explained that "only magic can defeat magic" and thus made Superman order him get his powers back. As the only way to restore legally removed magical Zarokian powers was to complete a series of Trials, Zyx and Superman-X went to do so while the others would distract Mordru.
Zyx and Superman-X completed had to complete three trials, giving a swamp monster his egg, solving a riddle, and avoiding to become encased in crystal, before Zyx's powers returned. When they approached Mordru, the other Legionnaires were transformed into grotesque beasts, but as Superman-X had learned a magic counter-spell from Zyx, he could rescue them.
With the combined powers of Zyx, Star Boy and the Council of Zerox, Mordru was encased in rocks, rendering him powerless.