Wikisimpsons - The Simpsons Wiki
Professor Frink had a vat ready to create metal robots based on a single element, and he was waiting for the perfect DNA to encode their personalties from. Bartman, standing near the VAT with a bag of laundry in his hand, accidentally set of his new sneezing powder Batarang, causing him to drop the bag into the vat. Suddenly a large explosion occurred and five robots appeared, based on the Simpson family.
Professor Frink called them corrupted, which, according to Holmium, "are fighting words", leading the robots to go off on a rampage. The robots visited the Kwik-E-Mart, where they were browsing the magazine aisle (Holmium reading Duff). Bartman tried to take them back to Frink's laboratory, but the robot's used their elemental features to counteract his moves. Holmium used his magnetic powers to steal one of Bartman's Bartarangs, though it was the soft jazz playing one, which distressed Homer.
Due to the similarity to his family, Bartman decided he couldn't hurt them, and they felt the same way. At that time, Gastro, a mutant created by Homer dropping his lunch bag into a radioactive vat, arrived causing chaos, which Bartman and the robots teamed up to defeat. Holmium, with the rest of the robots, tried to defeat it, but due to the large amount of chemical preservatives, they were insufficient. Bartman got Apu's expiry date changing sticker gun, and used it on Gastro, marking it to expire May 1995, causing him to blow up.
Later, back at the lab, the robots were in a glass box set-up, with a metallic version of the Simpsons' living room. Barium liked the room, but said it needed "an extra wide couch for Holmium's butt", which caused Holmium to strangle Barium a la Bart and Homer, complete with "why you little".