The Malach are a race of tentacled creatures that possess the living or undead. These creatures spread a virus in them, and the size of a pinhead or big enough to swallow your entire arm.
The Malach were used by Misao and Shinichi (Kitsune) in order to possess Damon and Caroline. Misao possessed Caroline to spread the Malach in town, so everyone could be infected. Shinichi used one on Damon. The Malach entered his body and took him over from the inside, corrupting his body and his soul, making him entirely under Shinichi's will.