Up until Ali was revealed to be alive it seemed very plausible that the visitations were by her ghost.
Hanna and Mona used a Ouija board. Hanna saw Ali.
A ghost went to visit Ashley on Halloween. She was one of the girls from the story about twins.
The creepy little boy from the doll hospital could potentially be psychic.
So I find it a little odd that people are acting like the supernatural elements only showed up when Ravenswood started. Frankly I'm a bit pissed about people throwing fits about it. Let the fans get some closure damn it. That show had more answers in ten episodes than Pretty Little Liars has had in over a hundred episodes.
Don't forget the doppelgangers. There's a new one. That patient at Radley named Donna looks a lot like Ali from the back.