I don't think that it's Peter. I don't want him to be a bad guy.

I don't think it's Peter or Deucalion. I think it's the cloaked stranger in the 4th promo in this link.

link

My gut doesn't think it's Peter. I don't really see any motive besides that he wants to get stronger. It would be too obvious though. Why would the writers recycle a villain from season 1? It's definitely not Deucalion he's on a whole other hidden agenda thing. And lastly that leaves Miss Blake...she's the most ambiguous character out of all of them. We don't know her past. The way she handles the situation when she discovers Derek is a werewolf is way too calm. She's strange...and not in a good way. Hmmm, my money is on her.

i know its missis blake aka jennifer

Its Ms.Blake she is not married. Besides thats not like Peter to go around killing innocent people and Decalion said that he would kill anyone that would get in his way.