From Penetentiary III. Not a monster, per se, but a ferociously strong murderous midget living in a prison. The film is highly recommended, too. I remember it playing on Joe Bob’s Drive In Theater back in the day on TNT. It’s gratuitous, deranged fun.
Watch it and I dare you not to go around yelling “Oak tree, Too Sweet! OOOOOAAAAAK TREEEE!” at least a few times.