Everything that happened tonight happened already.
Someone’s turning into a vampire? See: all of season 3. Also see: season 2, episode 21 with Jenna. This is supposed to be special and “out there” because it’s Elena, but people have been trying to turn her since season 2.
Bonnie saves an enemy’s life? See: season 1 finale. She saves Damon’s life (as well as Stefan’s), and then makes a declaration. Been there, seen that. At least last time “I know who I am now” went somewhere for a while, and the line held a lot of weight.
Klaus is in someone’s body? See: The time Klaus possessed Ric.
***Someone asked how Bonnie could transfer Klaus’ spirit in Tyler’s body, considering it took both Greta and Maddox to do it, and Greta was more powerful than Bonnie. I think the fact that it happened offscreen is the answer. She could do it because it’s convenient and fits the story JP’s struggling like a mofo to tell.
Car crash? See: the episode before Bloodlines where Elena crashed her car. They also parallelled it with her parents crashing, which…been there, done that.
Elena gets tricked? See: The Vampire Diaries.
Jeremy turns around, and there’s a ghost? See: season 2 finale.
Tyler loses his free will? See: the freaking story they just told.
As for dark!Bonnie:
I didn’t see anything. Bonnie talked in a mean manner to Klaus. I’ve seen her mad before. She saved Klaus’ spirit. So? Like I said before, she saved Damon in season 1. And that line she said? Means nothing. She had no choice. They never said she was willing to let her friends die, so…….the line means nothing. Not until we see her resist the Salvatores and actually take matters into her own hands. Are we even going to get the witches being mad at Bonnie?