How can this killer survive to the next movie? SPOILERS

So at the end of the movie, we find out this kid is going on to become the serial killer that is the bad guy of the movie Malevolence. So... the unique thing about this kid is some disease that means he can't feel pain, and evidently this was why the serial killer in this movie adopts him (I guess).

This is basically the core issue with leprosy - all or part of the body failing to relay pain impulses to let the sufferer know that they have an injury or infection. With modern medicine and vigilant self-awareness, it's manageable; in the old days, extremities frequently became infected and amputated.

I realize the writer must think "I feel no pain" makes a bad-ass serial killer, but in reality, it would make a dead serial killer. After the credits we see the kid many years later living by himself in a decrepit surrounding. The conditions this kid/killer lived in since he was six years old are an absolute worst case scenario for his disorder. Presumably you can't frequent the local hospital to treat all the injuries and infections that come from living in rotten, rusty environments not only filled with sharp edges but actively using sharp objects fighting with struggling victims.

So this is supposed to be one of the unique traits of this character... and it's actually a huge negative.... Not to mention that Bereavement really never makes any coherent effort to explain the serial killer who kidnaps the kid other than some generic skull he yells at and his scrapbook. It's very atmospheric in the cinematography, but clearly the director was more interested in atmosphere than making interesting characters. Granted, the leading lady provided interesting characters filling out her tank top and sheer pushup bra for the entire last half of the movie, but that wasn't worth listening to all the screaming.