A. The Mastiff (sometimes called the Old English Mastiff) and the Boxer are both magnificent breeds. When well socialized and bred by responsible hobby breeders, they make excellent family companions.
There is absolutely no good reason to cross these two breeds to create a big, powerful, unpredictable “designer dog.” Veterinarians, shelters and good breeders alike strongly discourage this practice. In fact, conscientious breeders will insist that pet owners spay their dogs to avoid accidental mismatings that will only add to the pet population explosion.