A dog is dragged into a sewer via his leash when his owner is pulled in. Later, we see the dead dog hanging from its leash in a basement, presumably killed by CHUDs. It's bloodied but looks like a bad puppet.
Cops aren't really portrayed in a positive manner. The only "good" cop is one of the main characters - the rest of the cops in this movie are shown as corrupt or just bad at their jobs.
Dripping noises in the sewer, panting and coughing of men struggling to breathe. The soundtrack can also have dense repetitive noises that can bother some viewers.
Yes, a character (who is intended to be delusional or psychotic) is very violent and overall not handled well. Lots of homeless people are portrayed in a bad light in this movie.