I signed up to respond to this. Mastiff mixes have been done all over the world and any of the ones that make sense have been pure bred in their native countries for quite some time. The only Mastiff mix that makes sense in America is the Great Dane for it's heat tolerance and need for healthier genes. The Great Dane is behind all of the heat tolerant mastiffs from the Tosa to the Fila to the Boerboel to the Bully Kutta, which you can see covers the globe. These dogs tend to have a high prey drive which isn't the best for mastiffs that aren't known for their obedience. The Great Dane is also behind the Giant Schnauzer which is known for obedience and doesn't shed, which makes for a great guard dog in the home. The Bernese Mountain Dog would be another great dog to add obedience to a Mastiff, but what these people really want are bragging rights and a trophy dog. These peope don't really have time to spend on training a dog, so the best mastiff for these people is a Tibetan Mastiff, something they can leave alone and doesn't need any training. The problem with that is they dont have the money or the character to control a Tibetan Mastiff. The Bandog is not American, it's already been played out in the Bullmastiff and the Boxer. The foundation Boxers actually look like American Bullys today. People just have these childish fantasies of the toughest dogs but never would have the money to travel to another country to see how grueling a Bully Kutta or Alabai fight is and these breeds don't even have the ideal structure. I could take a dog agressive French Mastiff and a dog agressive Alaskan Malamute and produce the perfect structure for bite force and endurance, but to what end? Having the most dangerous dog that could go through a door to kill someone like a Presa has to a woman that lived in an adjacent apartment in California. Even St Bernards kill people because they can be territorial and you can see them in the Alabai. Neapolitans and Cane Corsos have been tortured by Alabais and Bully Kuttas just because people have these fantasies about them. You can go on embarkvet.com and see the Cane Corso dna is a mongrel haplotype. Just take a Neapolitan and cross it with a Boxer and there you have a Corso. If you really want bragging rights look at a dog's haplotype and you will see it's unchanged origin.