He's a true brindle, at least on his head and legs - where each fur has more than one color. Fur on his body is sort of dirty brown color. I think he's too small for a mastiff - 35# at 5 months should be maybe 70-80# grown up. Also I'm not sure how many mastiffs are running around loose to get involved in a random breeding. Unless you mean mastiff as a type (like newfs, pyrs etc).

He's probably more than 2 breeds - we wondered about Akita too - would fit the brindle, narrow face and he has more of an Akita tail than a Chow tail. And his puppy coat is fluffy but not really long. But those ears are never going to stand up and neither Akitas nor Chows do "fetch"

COULD he have any newf in him? Do newfs fetch? (I mean they retrieve people out of the water don't they?)