while the first movie did have dark moments, i thought the fourth one was darker

Legend of the Saw Tooth Cave, no questions asked. How much darker it is is a big reason that I like it better than the first. I'd go into other reasons, but that's not what the poll is about.

Fourth one has a final battle, a death scene, assumed murder, and demonic entities. Yeah, its pretty fucked up

I wouldn't say that was a demon. It was most likely Daria's mother, not a spirit I would call evil. Her pack's alpha male was eviler than the ghost was.

A&O 4, obvious. First movie had it's moments but A&O 4 was the first of the franchise to embrace the dark element.