The Miniature Saint Bernard is not a purebred dog. It is a cross between the Saint Bernard and the Cocker Spaniel. 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.
"Johnny, pictured with me, was 3 years old when this picture was taken. He is obviously much smaller than a purebred Saint Bernard! He is 50% Saint Bernard and 50% Cocker Spaniel." Bred by Dakota Winds Ranch