Rust dragon

Rust dragons were planar dragons native to Acheron that had an insatiable hunger for metal.

Description
Physically, rust dragons resembled different metallic dragons from the Prime Material plane, such as silver, copper, and brass, except that their scales seemed to be covered by different forms of oxidation and their wings were thin with an iridescent character. Those differences were only in their appearance, as all rust dragons usually possessed a similar set of strengths and abilities.

The main sources of sustenance for rust dragons were ores and metals. They had a particular liking for adamantine, gold, mithral, iron, silver, and steel, but did not turn down other metals. They also enjoyed eating meat, particularly vermin, as palate cleansers between servings of different metals, in order to better appreciate their subtle differences in taste.

A minority of sages speculated that rust dragons might be related to rust monsters, but those claims were generally discredited.

Personality
Unlike pyroclastic dragons or howling dragons, rust dragons were not exceedingly aggressive or violent. They mainly attacked out of hunger, and even so only to the point where they could secure sustenance. Despite very focused on the task at hand and not tolerant of much meddling in their affairs, they were not above withdrawing from a hostile situation in which they had the disadvantage.

Combat
Any metal object that came in touch with a rust dragon's skin or its bite immediately rusted away into uselessness. They were also incredibly resilient against damage from weapons made of metal. Only extremely powerful magic weapons had a better chance of withstanding this rusting effect, but no weapon was completely immune.

Rust dragons possessed two breath weapons: a line of acid and a cone of extremely corrosive reddish-brown liquid that immediately destroyed any metal items that it touched. Only objects with some sort of magical enhancement could stand a chance of surviving it. They could also create effects similar to the acid fog, repel metal or stone, and wall of iron spells.

Society
Besides their home plane of Acheron, rust dragons could also be found in Banehold, Clangor, Dragon Eyrie, Hammergrim, and Nishrek. If found in the Material plane, they tended to build their lair in underground caverns near veins of metal, to the usual dismay of miners. They could be found alone or in families as they raised their young. Clutches of young rust dragons were also commonly found.