Aria is A: Theory from the Season 4 summer finale

'You do understand the function of the magician's assistant, don't you?'
'Yeah, she's there to distract 'em while he sets up his trick.'
'Well, you'd be right, if you weren't so wrong. While you're watching the magician –– that little innocent assistant is actually pulling the strings.' 

  • We now know that Ezra is A, or at least one of several A’s. So the above quote is eerily accurate when it comes to the summer finale. Ezra and Aria are a couple, and many people believe Aria is A too, because she potentially has multiple personality disorder which runs in her family. So in the above scene she is literally the magician’s (Ezra/A) assistant, who is in on it and perhaps even pulling the strings. 
  • The girls receive magic 8 balls from A, each with their names on a specific ball. Of course Aria’s ball is the one that says “A”.
  • In the second gif Aria of all the girls is the one who reads the message from A (as if she’s saying it herself), explaining that they are gonna watch her make a girl disappear. The camera deliberately focuses on only Emily and Aria while the note is being read. Later on at the magic show, Aria literally becomes the magician’s assistant. And just as Spencer says in the second last gif, Emily is the girl who disappeared… while they were watching Aria. "Watch me make a girl disappear”