Gauslime

It creeps across the ground drawing loose metal to itself, and the debris it accumulates armors and feeds it, absorbed slowly into the conductive sludge of its body. Its magnetism is its defense: it can suddenly repel or attract metal with enough force to fling away an attacker or yank a metal-toothed predator off balance. Sluggish and near-shapeless, it relies wholly on that magnetic trick and on being deeply unappetizing, and colonies of Gauslime gather at old ferrous outcrops, a cluster of glistening, metal-flecked lumps quietly stripping the ground of iron.