Metal Mimicry –The ability to become metal.
Colossus (Marvel) is a superhero that can turn his whole body into metal (Official Handbook of the Marvel Universe V1 #3).
Ferro Lad (DC) is a superhero that can only turn his skin into various metals (Adventure Comics V1 #346).
Shrapnel (DC) is a supervillain that can turn into metal shrapnel (Who’s Who in the DC Universe #13).
Ben Boxer (DC) can cover himself with metal coating (DC Who’s Who #2).
Batman (DC) becomes a metalloid in World’s Finest Comics V1 #143.
As mentioned earlier, Ferro (DC) and Colossus (Marvel) are the metal mimics of their respective universes and unite in Unlimited Access #2.
Flailing Dreadnought – Creature Collection II. Dark Menagerie
Guardian of the Damned – Creature Collection II. Dark Menagerie
Living Steel – TSR 2145 Monstrous Compendium Annual Volume 1
Metal Monsters – Space Family Robinson Gold Key #15 (1966)
Searing Wind – Creature Collection I
Shredstorm – D&D 3.5 – Monster Manual III
Xaver – TSR 2145 Monstrous Compendium Annual Volume 1
Metal Man (Savage Dragon) can turn into an immobile piece of cast iron.