Byrne and Giordano bring back the Metal Men’s most deadly enemy, as the team gets their first post-Crisis appearance in Action 590 (July 1987).
While touring a chemical factory, on a story with Lois Lane, Clark falls into a pit of waste fluids. Although not toxic, he notices a tingling sensation. The waste is the remains of Chemo, destroyed by Negative Woman during the Crisis on Infinite Earths, his mass had collected itself, but was unable to re-form. Until it got a taste of super-cells.
The Metal Men are re-introduced as Dr. Will Magnus acts all strange about a secret room in his lab. Platinum is too busy flirting to care. Gold, Iron, Lead, Mercury and Tin are all playing around with their usual banter, to Doc’s chagrin.
That all stops when Super-Chemo comes busting in.
Chemo has a number of Superman’s powers, thanks to the cell tissues that help make up his new form. The Metal Men also take new, combined forms, which was not so often seen in the past.
But even merged into a giant entity, they are no match for Super-Chemo. Superman sees the battle, and advises them to cut off the bring from sunlight, which charges his cells.
Without light, the super-cells lose their charge, and Superman uses his heat vision to boil Chemo away into steam. He does return eventually.
Tin gets destroyed in the fight, but the Metal men expect Doc Magnus to rebuild him, as he always does. Magnus refuses this time, to their shock.
This plotline continues when the Metal Men return in the book next year.