I just started to watch the series and I'm trying to catch up before season 5 starts. Without spoiling anything can anyone give me a list of season 4 must watch episodes to catch up on the basic mythology?
Honestly, there really aren't any non-mythology episodes on the show at this point. Every episode in some way has something to do with the larger over-arching story they're telling. From the last few episodes of season 3 and up to current, it's all connected.