(From the Wilderlands DMG pp 14-15)

Carbelium is a strange, lightweight but very hard red metal that is extremely rare. It’s only known source is on Gheulost Island in the Trident Gulf, which is protected by the Viridian Navy. The metal seems magically antithetical to iron and steel and is only slightly affected by magical protections. In fact, it is actually attracted to iron and steel (though it does not bond with it). It is too hard of a substance to be crafted into weapons larger than arrow heads. Some ancient wizards knew of a way to fuse small threads of carbelium into magical weapons, but those techniques have been lost. Presently, the only use for carbelium is in the making of special arrows for the Green Emperor’s elite archers. The arrows themselves are not magical, though the metal’s inherent properties make them seem magical.

Carbelium arrows: carbelium arrows are treated as keen weapons. Attacks with carbelium arrows are treated as a ranged touch attack ignoring non-magical armor and shields. Any magic bonuses from magical armor remains, but is reduced by 2. In fact, because carbelium is drawn to iron and steel, a target wearing metal armor grants the archer a bonus to hit based upon the amount of metal in the armor he is wearing. Subtract three from the AC bonus of metal armor to determine the circumstance bonus to hit that target. Thus, a target wearing a chain shirt grants a +1 bonus to hit, while a target wearing full plate grants a +5 bonus to hit. Though the arrows only do normal damage, they ignore any Damage Reduction that can be bypassed by any sort of metal such as silver, adamant, or cold iron, acting as the equivalent of those metals for the purpose of bypassing Damage Reduction. Carbelium arrowheads are essentially unbreakable and may be collected and reused in making new arrows. The ability to craft carbelium is only known by a few select wizards loyal to the Green Emperor and player characters may not craft carbelium items (presuming they manage to obtain carbelium in the first place) without permission of the Judge and specific training.

As a secondary effect, carbelium is a hazardous substance. Possessing more than a small amount of the metal (a pound or more) for more than one day requires a Fortitude save (DC 20) or the person suffers 1 point of both temporary Constitution and Intelligence damage. For this reason, even the emperor’s elite archers do not carry more than 20 carbelium arrows. Over time, those exposed regularly to quantities of carbelium lose their hair, their skin turns burning red and becomes scabrous and cancerous, their muscles slowly rot, their teeth fall out, their brains liquefy and they start to go insane.

Raw carbelium and carbelium ingots, as well as quantities of carbelium arrowheads, are kept in lead-lined boxes and chests, which protect the owner from the dangerous emanations of the metal. There have been attempts to make carbelium swords with lead-lined scabbards; all have failed spectacularly, and lethally. Carbelium is not available for sale in the general market, and can only be found most dearly on the black market (valued at over 1000 gp per arrowhead).