Blood Puppy

It's about a puppy that kills people. Not a whole lot of sophistication to it, but the puppy is too cute and people don't take appropriate action. Characters who know the puppy is deadly and maybe have even just seen it kill will still approach it in the hopes they can pet it. Character with gun? Sure they may aim, but you wouldn't shoot a cute puppy would you?

In this manner the film consists of the puppy slaughtering a few dozens of people until end credits.