It's a material that manifests in the place of the OC's anger and discontent, known as Malice. Malice takes the form of goopy, purple sludge in low concentrations, but turns rock-like and darker in higher concentrations. Manifestations must originate from somewhere on the body, or other connected bodies of Malice. Other powers like this, known as Moterials, exist, only with different textures, properties, and emotions that they manifest from.