Many trainers have bemoaned that fighting Bronzong is worse than fighting Spiritomb, for they resist a great many pokemon, and although they have a weakness they will not tell them which one. Some of these pokemon shrug off heat and fear nothing except attacks from below, while others are damaged by heat, but levitate over ground techniques. Some would rather try to crack a Shuckle, for these pokemon are some of the best defenders known to man.
Bronzor are found at many shrines for religious purposes, but the wealth of shrines has frequently made these shrines a target even in conflicts with no religious component, for holy items can fetch a large price on the black market. To protect worshipers and treasures alike, it has been common to foist the responsibilities of a temple guardian on a Bronzor, changing its form into a giant steel bell whose sound reverberates throughout whatever town they call home in a signal to take up arms.
Although Bronzong are skilled at self-defense, their true purpose of these pokemon and the "battles" they call a town's fighting men to is preservation. The battle is simply a means to buy time; Bronzong's tough defenses are another way to do so. Until they are knocked out, Bronzong will seek to gather and hide within themselves whatever relics of the gods their home shrine holds from looters, for these pokemon are hollow. And their immunities are designed not to make them difficult to fight, although few priests would complain about this fact, but because fire and structural collapse are the greatest dangers to a pokemon gathering items from a temple under siege.
Thankfully, the age of war has finally passed, and this pokemon's secret can be shared not only among priests, but with the rest of humanity.