Call them ghosts, call them demons, call them creepy girls that crawl out of TV sets - they are that catchall category of paranormal horror creatures. Not only do these not hold up to scientific rigor, they are barely internally consistent with their own made-up rules.
The most glaring issue is: how does an entity that can pass through walls manipulate physical objects? We've already debunked telekinesis and magic, so we know ghosts aren't using those means. Even if you argue that ghosts are able to generate powerful electromagnetic fields, that would still put a limit on their capabilities - for instance, how would they move a wooden door?
A ghost must thus be moving objects with physical forces. When you throw a ball - or a knife - your are imparting momentum into the object. You generate the force of movement with your body, and it is your body pushing against the object that transfers the momentum. If a ghost passes through an object, then it can exert no force on it, and thus cannot manipulate it.
From The Texas Chainsaw Massacre's Leatherface to Friday the 13th's Jason Voorhees, slasher films will sometimes rely on giving their villains superhuman abilities to make them even scarier - because apparently the sadistic side of man isn't frightening enough. Since we've ruled out the possibility of magic and ghostly possession, that means we can't explain any superhuman feats through supernatural means. Thankfully though, there are examples of actual superhumans in the real world.
Finnish skier Eero Antero Mäntyranta had a gene mutation that caused a tremendous increase in his red blood cell count, which allowed his blood to carry up to 50 percent more oxygen and thus lend him superhuman endurance.
Dr. Yuree Vajramuni possesses superhuman strength. Through years of physical conditioning, he built up bone mass in his legs, making them strong enough to snap multiple baseball bats in half without shattering. Through mental conditioning, he made himself able to suppress the self-preservation instinct that limits human beings from using their full strength. But even then, he isn't strong enough to casually toss human beings across a room - he was able to activate 96 percent of his leg's musculature on command, which sounds high, but a non-superhuman control test activated 89 percent. Stronger than normally possible, yes, but not unbelievably strong.
Some people are born with a congenital insensitivity to pain, which may be regarded as a superpower by some. Certainly, a killer who isn't deterred by a swift kick to the groin is a cause for concern.
So let's say that our killer coincidentally has the perfect cocktail of traits to make him superhuman: he's tall, he has a large frame, his bones are extra thick, he doesn't feel pain, he's very strong, he can run with a chainsaw for a long time without getting tired... That's all well and good, but there's no genetic mutation, congenital condition, or martial arts training that can make him immune to bullets. Or fire. Or asphyxiation. Or 17 stab wounds in the back. You can ignore pain all you want, but damaged muscle tissue will slow you down, and organ failure will stop you dead in your tracks.