"Brewski the Mountain Mastiff at 10 months old; about 120 pounds and very tall—he is still a little lanky and leggy, but starting to fill out and thicken up, especially in the front quarters and chest. He has an amazing temperament, great personality, loves EVERYONE and other dogs and my cats, too, but they do not particularly like him much!"
The Mountain Mastiff is not a purebred dog. It is a cross between Bernese Mountain Dog and the Mastiff. The best way to determine the temperament of a mixed breed is to look up all breeds in the cross and know you can get any combination of any of the characteristics found in either breed. Not all of these designer hybrid dogs being bred are 50% purebred to 50% purebred. It is very common for breeders to breed multi-generation crosses.
Brewski the Mountain Mastiff (Bernese Mountain Dog / Mastiff mix) puppy at 3 months old
Brewski the Mountain Mastiff (Bernese Mountain Dog / Mastiff mix) puppy at 5 months old on the sofa with his stuffed toy duck
Goober the Mountain Mastiff at 9 months old, weighing around 90 lbs.