→Serana is invincible
Also when i say invincibility i do not mean she is essential, i mean no damage can be done to her, exactly the same as knight-paladin Gelebor. Attacks go through her, moving into her will not cause her to move and shouts and magic pass through her. While this is actually quite good as she can be an invincible distraction, she can easily trap you in a room. I play on PS3 so i cannot fix it, but i know PC players can use setghost 0 to fix the problem.
PS: does anyone know why returning there sets ghost to 1 (true), is it so nothing can damage her while she is trapped in the stone chamber.