When it comes to finding synonyms for the term "mastiff puppy", there are several options to choose from. The first synonym that come to mind is a Tibetan Mastiff puppy, which is a large dog breed that originated from Tibet and is known for its loyalty and protective nature. Another synonym could be a Bullmastiff puppy, which is a cross between an English Mastiff and an English Bulldog and has a strong, muscular build. You could also refer to a Neapolitan Mastiff puppy, which is a majestic and powerful breed that originated in Italy. Alternatively, you could use the term "Molosser puppy", which refers to any large dog breed that has descended from the ancient Molossus breed. Overall, there are several synonyms for the term "mastiff puppy" depending on the specific breed and characteristics you want to emphasize.