Meth (Methacrylate) was a plastic android created by a villain calling himself 'Professor' Bravo. The Metal Men fought Bravo's 'Plastic Perils', while Bravo taunted them because "Plastics are the future". Finally, Gold read up on plastics and learned of their low melting point, so the Metal Men poured molten metal on the androids, destroying them, and captured Bravo.
