For reasons that have never really been clear, there are some folks who feel the need to label horror movies as anything but what they are.
In this case, though, there is a valid argument to be made that Joker isn’t quite a horror movie, though it veers into that category.
For me, though, I do believe the final moments of the movie echo the sort of unleashed terror that you’d typically find in a horror film.
The burning sense of danger and the knowledge that no sense of relief will be found for its story makes it feel like a horror movie at heart — the sort of madness that would make the title character cackle with deranged glee.