Strange monster built like a huge turtle with insectoid head and feather-like antennae

A rust monster (sometimes known as a corroder or corrosion beast) is a strange monster built like a huge turtle, with an insectoid head sporting large feather-like antennae and a thick tail with a hammer-like protrusion at the tip which seems to serve no purpose whatsoever. The touch of any part of a rust monster's body oxidizes metal objects instantly, turning them to rust, verdigris, or other oxides as appropriate. One attacks with its antennae, brushing them over metal items. Non- magical metal attacked by a rust monster, or that touches the monster (such as a sword used to attack it), is instantly ruined. A hit with a non-magical metal weapon inflicts half damage before the weapon is destroyed. Magic weapons or armor permanently lose one "plus" each time they make contact with the monster. The metal oxides created by this monster are its food; a substantial amount of metal dropped in its path may cause it to cease pursuit of metal-armored characters. Use a morale check to determine this. Metals that do not normally oxidize, such as gold, are of no interest to a rust monster and will be ignored. While rust monsters will consume oxides of silver or copper, they have a strong pr

Magical, armadillo-like creatures with long tails and two long, antennae-like feelers. Feed on rusted metal.

Strange monster built like a huge turtle with insectoid head and feather-like antennae

Rust monsters are creatures vaguely resembling a 5-ft long and 3-ft tall giant bug-like armadillo that weighs about 200 lbs. Rust monsters have rust-red colouration on their dorsal hides, yellowish tan on their ventral hides, and two prehensile antennae on their heads. Rust monsters are only found in underground type environments, which they prowl constantly in search of food. Rust monsters consume metal of any kind, especially ferrous metals and ferrous metal alloys. The antennae of a rust monster can "smell" metal 90-ft away, and the creature will dart toward such a source of food with blinding speed, rolling 2 attacks with its antennae at the largest piece of metal it can sense. A successful attack causes up to 10 cubic-ft of metal instantly to crumble into easily-digestible rust and the creature will immediately cease attacking in such a case and begin devouring its newly-created meal. Metal with magical bonuses gains a 10% chance per plus of not being affected by the rust monsters attack. For instance a +3 shield would have a 30% of resisting the rusting effect. A successful "to hit" roll against a rust monster with a metal weapon automatically subjects that weapon to a rust