These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Complete Monster: The serial killer loves playing cat and mouse games with his victims. He infiltrates a group of FBI profilers during a field mission to a deserted island with a makeshift town used as a training ground by the bureau, where they must solve a case involving a fictional serial killer called "the Puppeteer" organized by their supervisor. He sets the island up with an array of boobytraps and puzzles to kill them while watching from within the group to turn them against each other and give himself good sport. His more cruel murders include a victim getting slowly killed with liquid nitrogen from the feet up, and another one burned to death from inside through acid-laced cigarettes. He kidnaps the supervisor (who had been monitoring the group in secret) to an abandoned warehouse on the other side of the island where he proceeds to torture him for days before preparing his corpse and hanging it up for the trainees as a sort of perverse puppet. It's only after his identity as Sarah's best friend Lucas is revealed that the true level of his manipulation becomes apparent, and he frankly admits he started his string of murders by killing his parents as a child and now simply enjoys a good hunt for new and more intelligent victims.
Seeing Harris strung up to the ceiling, hanging by his face and limbs with hooks and wires was bad enough, but an alarm goes off that causes his body to jerk around like a puppet while children's music creepily plays.
The first murder, involving the victim getting sprayed with liquid nitrogen until they shatter into pieces, would not seem remotely out of place in a Saw film.