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Nightmare Fuel: Dredd
The three drug dealers being skinned alive and tossed to their deaths. Being skinned alive is bad enough (we even get wince-inducing glimpse of skin being sliced off), but the use of Slo-Mo means they fell for what seemed like hours, in agonizing pain, and unable to do anything about it.
Another idea is that they got Slo-Mo before they were skinned alive, so both the skinning and the falling was dragged out for a long time.
On the same note, Dredd's execution of the drug-user at the beginning; namely, firing a Hot-Shot round (read: flare) into his mouth. We get to watch his head graphically being burned from the inside out.
Ma-Ma. A hyper-violent, scarred-up, crazy-as-hell woman with a bias towards brutal murders and has absolutely no problem killing everyone in Peach Trees to kill Dredd.
Most of the death scenes have no Gory Discretion Shot at all, leaving quite a few mutilated corpses for the audience to stare at.