The "Death Wraiths" - a.k.a. "Smoke Creatures" or "Phantoms" - are a race of spectral creatures made of suspended gas particles. They have the ability to psychically project themselves in the past and influence minds to some extent. In one alternate timeline, they have dominated and devastated the Earth by the year 2008. However, the Doctor in the 19th century described that as a highly unlikely future. The Wraiths attempted to use their psychic abilities to invade other timelines as well, but to no avail.