@Riger : yeah the gelatinous cube, you think you find a magic weapon floating in the air surrounded by a mystical looking shiny iridescent fog and when you extend you arm to reach for it, you feel that you skin is starting to disolve in a violent acid and it is stuck to something that slowly crawl along your forearm to your elbow, then your shoulder as your finger's bones are starting to appear beneath the half disolved skin and muscles ...
Of course gelatinous cube doesn't digest metals...
Most oozes and slimes continue to grow as long as they can find enough food, and they can eat mostly anything organic and quite a few minerals (and their stats goes up each time they grow), they can't be affected by age or illness and usually divise themself unto mutliples smaller entities after some time but there are simple spells that can block their division ability definitively, making them grow forever...
So sometimes you can find some supermassive ones that can give a trashing to a dragon (and I don't mean building sized, I mean city sized or more).