We could not find any reputable source that could provide information on an "Assyrian Mastiff." However, it seems that there are no known breeds of dog specifically called "Assyrian Mastiff." It is possible that the term is a made-up name or a regional nickname for a particular breed of dog in a certain region. Or it could be a crossbred dog made by breeding two different breeds. Without adequate information, it would be difficult to explain precisely what an "Assyrian Mastiff" is or looks like.