Koffing will eat almsot anything to convert it into toxins and gases in its body. Don't let it near fire or electricity, because the gas can be flammable. They tend to smell pretty rancid... I've known of a few cities that had Koffing swarms.

As for the sword... that would be a Honedge, most likely. It's part Ghost, so it might not eat very much, but sometimes giving it some scrap metal might be a good treat so it can repair any nicks or scratches it gets. Just don't touch the sash - it'll drain your life energy.