I've never posted but always read your theories. I've been thinking all day and I think there's a lot of clues that point to Spencer having multiple personalities rather than her having a twin. If it IS Twincer I think the scene in the promo with Wren having a gun is him shooting Twincer so that she has a wound. If not, I think AD stands for After Death as in someone we think is dead but they aren't or someone "became" someone new if that makes sense lol.
Omg I love that!! Twincer is like “I’m so jealous of my sister’s life, I want to go hook up with Toby, but in order to do that, I need a wound on my shoulder to look like her. Shoot me Wren” and that’s why Wren was so scared to pull the trigger. This is suchhhhh an amazing idea, good one. It’s so twisted because why couldn’t Twincer just draw a fake wound with makeup or whatever? But it makes sense especially because we saw Twincer and Wren at the airport so we know they’re working together.