http://www.islandpacket.com/2012/04/05/2026201/boy-3-mauled-by-bull-mastiff-on.html
While I love Mastiff's, there are certain ones I wouldn't own and those are the ones that are genetically more apt to be aggressive. Like the Bullmastiff.
http://www.happylegsbmf.com/documents/gamekeepers.pdf
However, unlike the Pitbull group, Mastiff people don't want every Tom, Dick and Inbred Harry to own one of their beloved dogs. Hence, more likely to point out the cons of owning their breed besides important information for the potential owner.
http://www.bullmastiff.us/AboutBullmastiffs/About.html