Trait: Magnet pull.
EVs: 252 special attack, 252 speed, 4 special defense.
Hidden Power Fire.
This set was made to destroy Bronzong. Magnezone easilyout speeds Bronzong and uses Magnet Rise. Bronzong uses Earthquake and sadly misses. Then within four turns the match is up.
4 special Atk Bronzong Earthquake vs. 0 HP / 4 special Def Magnezone: 11-16 (3.1-4.5%) -- One of the worst moves ever.
252+ SPA Magnezone Hidden Power Fire vs. 242 HP / 0 SpD Bronzong: 112-124 (35-37%) -- guaranteed 4HKO
Note: These are not the actual figures. But they are around the smae number.