The rust-buster is a rare mutation that occurs only once every few hundred years – a rust monster that, by some quirk of chance, is somehow capable of devouring magical metal. The arcane energies that find their way into these monsters’ diet permeate their bodies, granting them unnaturally long lives and
swelling them to great size. Rust-busters are much more
aggressive than their smaller kin, and slightly smarter, able to coordinate ambushes and track their prey over large distances.