I don't want any more long lost DiLaurentis family members. Charlotte is the one and only.
Who I think Big Bad could be:
* Mona winning back the game. Remember she said she's "still winning the game". So basically it's possible she will win back her dolls 5 years later
* Lucas is somehow connected to all this. I think he may be Bethany's twin. Or Sara's?
* Peter Hastings knew about Charlotte and Mrs. D and this entire thing and is the new Big Bad aka killer.
* Jessica has a crazy twin.
If the new big Bad calls themselves -A it's probably Lucas/Mona. If not, then Peter Hastings or Jessica's twin.