cybermen have a number of weaknesses over the years. their biggest weakness is gold. it was not mentioned that they did not like gold until their attempt to destroy the planetoid voga (the so-called "planet of gold") in "revenge of the cybermen" (1975). initially, it was explained that, because it is very hard to grind up, gold chokes their respiratory systems. for example, the however, in later serials, gold appeared to affect them rather like silver affects werewolves, with gold coins or bullets with gold on the edge fired at them having the same effect. the revived series' cybermen have no weakness to gold.