Magnezone is Barret's main and most reliable Pokémon. He used it while battling against Ash and his friends, who were trying to stop the Grunts from getting to N, Anthea, and Concordia. Magnezone battled against Ash's Pignite and Oshawott, and proved to be quite strong by being able to defeat Pignite despite the double type-disadvantage. Ash then used Pikachu, whose Electric attacks subdued Magnezone's ones, taking it out.
It was used in the next episode to fight Team Rocket. After Barret and Aldith were trapped by Team Rocket, Magnezone used Supersonic to confuse nearby Pokémon causing them to attack the machines creating the cage.