On Zarok, the Sorcerer's World, the High Council is reviewing the misbehavior of young Zyx. They strip him of his powers with mystic bands, and he can only remove them by proving himself worthy and completing a trial. They're interrupted when a powerful sorcerer enters the chamber: Mordru, returning from his banishment. Despite the fact he was given the same bands, he found a long-lost talisman, the Lamentation Pentacle. He uses his powers to ensnare the High Council, which are powerless against him. The High Elder sends Zyx to get help, teleporting him out of Mordru's grasp. He arrives on a Legion Cruiser and tries to explain what happened, but they're skeptical. They finally agree to go, only for Zyx to have to explain he has no powers.
Mordru begins to drain the elders of their magical power as the Legion arrives on Zarok. Zyx warns that only magic can defeat magic but refuses to go through the trial to get his powers back. The team splits up: Superman leads the team against Mordru and Kell-El ends up being volunteered to help Zyx on his trial. Zyx activates the bands on his wrist, where a projection of the White Witch directs him to the Cave of Lore. They depart and Mordru's magical army closes in on the other Legionnaires.
Heading toward the cave, a giant monster confronts them in the swamp and Kell-El discovers that his powers are gone. The creature eats Kell-El and Zyx tries to go after it. It spits out Kell-El and as they run, Zyx spots eggs suspended from a tree. He figures out the creature is trying to protect its young, and when it knocks Kell-El into the tree, they save the eggs. Kell-El begins to sink into the mud and Zyx rescues the eggs and hands them over to the monster. The White Witch projection appears to tell Zyx he's passed the first trial.
Mordru arrives to confront the Legionnaires and Superman attacks him. Mordru is more then resistant and overwhelms the team with his magic. Kell-El suggests he learn a counter-spell from Zyx without much luck. They proceed through the Cave of Lore and come to a vault door, where the White Witch offers them a riddle. As Zyx considers it, the cave ledge they're standing on begins to fall into the lava below. Zyx tries to work out the riddle and manages to solve it with seconds to spare. The door opens and they get into the next chamber just in time.
In the next chamber, all the wizards who have failed the trial are encased in crystal. Crystal hands emerge to entrap them as well but working together they get into the next chamber where it turns out they have passed the test of teamwork. Zyx's powers are restored and he teleports them to confront Mordru. The sorcerer turns the Legionnaires into magically mutated monsters and Kell-El holds them off while Zyx goes after Mordru. Kell-El manages to cast the counter-spell, reverting the Legionnaires back to normal. They attack Mordru and manage to overwhelm him, and Zyx takes the Lamentation Pentacle from him. The High Council is restored and with Star Boy's help they imprison him deep within the planet. The Council congratulates Zyx and gives him a magical helm to represent his achievement. Zyx thanks Kell-El as does the Council… especially for putting up with the imp.
Mordru first appeared in Adventure Comics #369 (June 1968), and was created by Jim Shooter and Curt Swan. He staged a coup over the sorcerers' planet of Xerox and built an empire throughout space, until he was defeated by the Legion, who sealed him within a vault. He since went on to be released, attempt to achieve universal domination, and be defeated by the Legion. His powers waxed and waned over the years, as has the amount of control he has over his empire.
In recent years it was established he was a renegade Lord of Chaos with vast powers and who has existed since the dawn of time and will live until its end. Most of his battles have been in the 21st century against the JSA. Mordru has vast powers that allow him to hold his own against any superhero or team of same. His one weakness is his seemingly psychosomatic fear of confinement: entombing him strips him of his powers.
The White Witch first appeared in Adventure Comics #350 (November 1966) and was created by E. Nelson Bridwell and Curt Swan. Her name was established as Mysa Nal, the sister of Dream Girl. Although growing up on a planet of precognitives, Mysa had no ability to see the future and traveled to the Sorcerers' World, Zerox, to learn magic. There she led a rebellion against the conqueror Mordru, and was transformed into a hag. She later regained her youthly form and aided the Legion on occasion, finally earning membership during their battle with Darkseid. Subsequently she married Mordru and became his queen. In later retcons she was established as the daughter of Mordru with no relation to Dream Girl. In the current continuity as of the time this episode aired, she is a member of the Wanderers and her plant of origin is unknown.
Although White Witch's powers have varied over the years, as a Legion member she had the ability to retain a limited number of spells, covering a wide range of affects. She could sustain people in the void of space, levitate, and cast mystical bolts. The exact limits of her powers were unknown and sometimes varied considerably.