What is Miasma?

Miasma, is the remnants of "The Last Spell" cast by the Council of Lords Mages. Dark, twisted, both living and unliving. It draws on the energy of life to sustain itself, yet can go years without a fresh source of energy without growing, without shrinking, and without weakening. Attacking the Miasma itself does nothing to any structure or being made of, or covered in it. Fluid in its make up, yet harder then Adamantium it flows around anything it has corrupted like blood in a vein.