That Billis actually during his introduction to the demon Abidon he says that the world will die beneath its shadow, he did mean literally as we saw everyone die as soon as the demon's shadow covered them. I never noticed that at all the first two times I watched this episode. He also mentions that Alderon is the son of the great beast (the huge demon from that Doctor Who episode where it was presumed to be Satan chained inside a planet) this demon was Satan's son, chained inside The Earth under a time rift to stop him from going any where.