The below trailer was released shortly after the panel in SDCC.
I'm very anxious to see how the Spirits book takes off. I could theorize possible negative spirits bleeding over into their reality. Perhaps someone trying to interfere with specific spirits again, much like with the koi in ATLA, season 1.
I also noticed some familiar faces, and these are just the ones in the first trailer! I'm rather curious to see how Won Shi Tong plays into the storyline. Always one to hold a grudge, it's probably not in her favor that Aang left him with such a bad taste in mouth. Spirits in the past haven't hesitated to hold the current avatar responsible for previous avatars actions. It could make for some interesting exchanges, I wonder what needs to be fetched at the library, or perhaps stored?
What are your guys' thoughts? What stood out to you?