5) Slow Mutants
In The Gunslinger, Roland and Jake travel beneath a mountain during their quest to track down The Man in Black and encounter a group of slow mutants along the way. In a sequence lifted straight out of a horror movie (see: The Descent), the duo find themselves being chased down in the pitch black by these horribly mutated and feral humans, and this is something which could work really well as a set piece in The Dark Tower.
We already know that Jake is going to end up paying a visit to Mid-World, and while Roland will encounter some pretty awful monsters in the form of the Can-toi – rat-faced beings who wear human masks – it definitely wouldn’t hurt to throw this lot into the mix. They’re not an integral part of the books, but utilizing them fairly early on to get moviegoers on the edge of their seats and show what a badass Roland is would be a wise move.