Like his Justice Society teammates, Doctor Mid-Nite had a tall order to handle. His Earth-Two Metal Men adversaries consumed copper and adopted the attributes of that particular element. How would he defeat a mini-armada of such foes?
Turned out that while making his dimwitted enemies, Doc tricked them into replenishing their energy eating copper fixtures which gave them sore stomachs. Too much isn't a good thing, guys!
Mercury, the sarcastic member of Earth-One's Metal Men, was also its most pliable and adaptable. Rather than get poisoning from getting to close to another element, he proved a mastery of form and fluidity, literally!
Although it must be said his salty disposition at times wore thin with his teammates, he nevertheless proved a valuable asset, all incarnations of him including his later replacements as each model expired.