The Metallum comes in three categories: stalks, filaments, and sheets. The stalks are the most important part of a given Metallum entity, and spend all their time collating and distributing information from all the filaments and sheets, making new filaments, and processing input. Stalks get bigger the more their filaments and sheets feed. While the Metallum is a hive mind capable of re-growing itself from even the smallest fragment of a filament, it tends to do most of its information and stimulus processing in the stalk, so destroying the stalk will incapacitate it for a time. This “stun state” can allow the enterprising adventure to collect, destroy, or imprison whatever filaments remain. Stalks are not as mobile as filaments or sheets, and a given Metallum stalk will always be extremely well-hidden, often on a completely different planet or plane from its associated filaments and sheets.
The filaments are the smallest living pieces of Metallum anyone is likely to encounter “in the wild”. They typically appear as insect-like forms varying in size from a handful of centimeters long to several meters long, but this is not their native form, it is only their most effective combat form against humanoids, and thus the form in which they are most often seen. When not fighting, The filaments much more closely resemble the name we have given them; they are incredibly long and so thin as to be nearly invisible. In this form they earth glide through rock seeking out ores to consume. Once destroyed, filaments can be worked into useful items, but only in a furnace stoked by the amniotic fires of magma dragon eggs.
Sheets are combinations of filaments, and are formed primarily when a given Metallum feels threatened, or needs to operate on a larger scale for whatever reason. Sheets are fast, strong, and stupefyingly dangerous. They can grow to be as large as a planet, though it is not known if that is the limit to their size, or if they just have never needed to get any bigger. Regardless, it is folly to attempt to fight one directly.
As a living silicate outsider, the Metallum has both a soul and an intelligence and thus can be affected by enchantments and other mind magic, though its unique hive mind attributes make it especially resistant to those types of spells. Once a day, any given filament can absorb and/or disenchant a weapon that strikes it. Filaments are very resistant to damage, and weapons that slash or pierce (including bolts and arrows) are next to useless. Force damage is by far the most effective means of fighting them, if one is compelled to do so.
The best way to communicate with a given Metallum entity is via pure telepathy, i.e., telepathy using pure sensory input, rather than language, or by contacting it on the astral plane where neither you nor it may harm one another. The metallum is quite aware of the usefulness of its own flesh, and as such is quite wary of other species, especially those that craft and wield tools.